Ventricular Septal Defect (VSD)

A ventricular septal defect (VSD) is an opening in the interventricular septum allowing blood flow between the left and right ventricles. VSDs are, by a clear margin, the single most common congenital cardiac malformation — though they frequently occur alongside other lesions (as part of tetralogy of Fallot, double-outlet ventricles, common arterial trunk, or transposition) as often as they occur in isolation.

Classification: Border First, Then Location

The modern, echocardiographically useful classification organizes VSDs by their border type first, since this determines both surgical approach and proximity to the conduction system — and only secondarily by which right ventricular component (inlet, trabecular/apical, or outlet) the defect opens into. A defect of any border type can, in principle, open into any RV component, which is why a two-tier classification is more precise than a single flat list of “types.”

• Muscular defects — a completely muscular border, unrelated to any valve. Can be single or multiple (the “Swiss cheese” pattern) and occur anywhere in the septum. Distinguishing a muscular inlet defect from a perimembranous one matters surgically: the conduction bundle runs anterosuperior to a muscular inlet defect, but always posteroinferior to a perimembranous one.
• Perimembranous defects (the precise term — not simply “membranous”) — part of the border is fibrous tissue at the junction between valve leaflets and the central fibrous body/membranous septum. The true membranous septum is a genuinely tiny structure; a defect confined to it alone would be too small to matter clinically. These defects can extend toward the inlet, trabecular, or outlet component, or be confluent across more than one. A perimembranous defect extending into the inlet component has historically been called an “isolated atrioventricular canal-type” defect — a misleading label, since these hearts have none of the atrioventricular septal deficiency or common AV junction that defines a true Atrioventricular Septal Defect.
• Doubly committed juxta-arterial defects — fibrous continuity between the aortic and pulmonary valve leaflets (or override by a common arterial valve, as in truncus arteriosus), because the outlet septum and the septal component of the subpulmonary infundibulum are both absent. Aortic valve prolapse into the defect is common, sometimes contributing to spontaneous size reduction but also a frequent cause of progressive aortic regurgitation.

A true LV-to-right-atrium communication (a Gerbode-type defect, through a deficient atrioventricular membranous septum) is genuinely rare — most apparent cases are actually a cleft or deficient tricuspid septal leaflet adherent to a perimembranous defect’s margin, producing the appearance of LV-to-RA shunting without true membranous septal absence.

Physiology: Pressure vs. Flow Restriction

VSDs are broadly divided into small, moderate, and large — defined by their effect on pressure and flow, not by a single fixed pressure gradient:

• Small VSD — pressure-restrictive, maintaining a normal RV pressure. Notably, a substantial left-to-right shunt can still occur through a small, pressure-restrictive defect as pulmonary vascular resistance falls over the first weeks of life.
• Moderate VSD — still provides some resistance to pressure, but comparatively little resistance to flow.
• Large VSD — offers little resistance to either pressure or flow, so RV pressure runs near systemic levels and the left-to-right shunt is large. Over time, this drives pulmonary vascular resistance up until it exceeds systemic resistance, reversing the shunt (right-to-left) and producing Eisenmenger syndrome with cyanosis.

Associated lesions are common, not the exception: in surgical series, nearly half of all VSD patients have an additional cardiac anomaly. Atrial septal defect (including PFO), pulmonary stenosis, and a persistent left SVC are seen in roughly 13%, 15%, and 8% of VSD patients respectively, and patent ductus arteriosus is also frequently associated. Double-chambered RV and subaortic stenosis, together or separately, occur in up to 10% of patients with a central perimembranous VSD.

Clinical Findings

• Auscultation — a harsh, holosystolic murmur at the left sternal border. Counterintuitively, smaller defects often produce louder murmurs — higher-velocity, more turbulent flow through a more restrictive orifice.
• ECG — left atrial enlargement and LV hypertrophy from the chronic volume load, reflecting the left-sided chamber enlargement pattern that distinguishes VSD from ASD (which volume-loads the right side).
• Chest X-ray — cardiomegaly (LA, LV, and PA enlargement) with increased pulmonary vascular markings from pulmonary overcirculation.
• Cardiac catheterization — an oxygen step-up at the RV level compared with the RA confirms the shunt location, and permits direct Qp:Qs quantification by oximetry.

Echocardiographic Findings

Echocardiography has become the universally applicable modality for diagnosing a VSD, covering both anatomy and hemodynamics. 2D imaging — using several windows, planes, and sweeps together — is the mainstay for examining the whole ventricular septum, with 3D imaging and color and spectral Doppler added.

Preoperative Assessment: Key Elements

Anatomy: determine the VSD’s type, location, size, and number; show its relationship to adjacent structures (the tricuspid, aortic, and pulmonary valves) and whether any valves are in fibrous continuity; and use 3D where it helps define the defect’s geography and its margins for device closure.

Hemodynamics: document the direction of flow across the defect with spectral Doppler; estimate the degree of restriction and RV systolic pressure from the peak velocity across the VSD; cross-check RV pressure with the tricuspid regurgitation velocity and the ventricular septal curvature at end-systole; judge the volume load on the left heart from LA and LV size (tracking z-scores over serial studies) and LV systolic and diastolic function; and identify the cause of any restriction, such as tricuspid valve aneurysmal tissue or aortic valve prolapse.

Associated lesions to look for: an RV muscle bundle (double-chambered RV), a subaortic membrane, and a prolapsing aortic valve leaflet.

A View-by-View Approach: The Sweeps

Because the septum is a curved, three-dimensional structure, each window is used as a sweep rather than a single snapshot.

• Subxiphoid long-axis (frontal) sweep. Progressing superiorly, it profiles the atrioventricular canal (inlet) septum and the membranous septum; advancing superiorly and anteriorly, it shows the muscular septum.
• Subxiphoid short-axis (sagittal) sweep. Shows the conal (outlet) septum as well as the muscular septum.
• Subxiphoid left anterior oblique sweep. Gives anatomic visualization of the defect’s size and the degree of restriction, and shows how it relates to the septal/anterior commissure of the tricuspid valve.
• Apical four-chamber sweep. Start posteriorly, in the plane of the coronary sinus and AV valves, so a posterior or inlet defect isn’t missed. This view shows the AV canal (inlet) septum above and the posterior and mid-muscular septum below; sweeping anteriorly brings the membranous septum into view at the septal/anterior commissure of the tricuspid valve, and continuing toward the outflows shows the outlet and anterior septum.
• Parasternal long-axis. Transects the aorta and LV and shows the mid and apical muscular septum. Tilting toward the tricuspid inflow shows the membranous and inlet septum; tilting anteriorly toward the pulmonary outflow shows the conal septum and anterior muscular septum.
• Parasternal short-axis — one of the most important views for determining VSD type. At the base of the heart, with the aortic valve as a clock face, the membranous septum lies between the tricuspid valve hinge point (9 o’clock) and 11 o’clock, and the conal septum lies between 11 o’clock and the pulmonary valve hinge (2 o’clock). As the sweep moves toward the apex, the muscular septum is profiled.

Imaging by Defect Type

• Central perimembranous VSD. Seen adjacent to the septal/anterior commissure of the tricuspid valve on the RV side, and the commissure between the right and noncoronary aortic cusps on the LV side. The subxiphoid left anterior oblique sweep shows size and restriction; the apical four-chamber view with anterior angulation, between the septal tricuspid leaflet and the aortic valve, also shows it. In the parasternal short-axis view at the base it lies between the tricuspid annulus (9 o’clock) and 12 o’clock. Tissue from the septal tricuspid leaflet can shroud the defect and restrict the shunt — and can mask the defect, so 2D underestimates its true size. Subxiphoid short-axis and right anterior oblique views help assess an associated double-chambered RV.
• Inlet VSD (perimembranous or muscular), located along the length of the tricuspid valve. A lack of a muscular rim between the tricuspid valve and the defect distinguishes an inlet perimembranous (AV-canal-type) defect from a posterior muscular one. Subxiphoid sweeps show it below the AV valves but often not in its entirety, since the sweep plane cuts through the defect. In the apical four-chamber view the defect is posterior and the normal mitral–tricuspid offset is often absent; still, seeing both a tricuspid valve and a mitral valve excludes an AV canal defect. In parasternal short-axis it sits in the posterior septum between 7 and 9 o’clock at the level of the tricuspid and mitral valves.
• Outlet VSD. Well seen on the subxiphoid short-axis view, with flow directed from the LV toward the pulmonary valve because of the defect’s location. When the conal septum is completely absent, the aortic and pulmonary valves are in fibrous continuity and appear at the same level. On the apical and parasternal long-axis views it can look like a central perimembranous defect, only more anterior; the parasternal short-axis view at the aortic valve level is one of the best ways to tell them apart — outlet defects sit at about 12 to 2 o’clock. Look for right coronary cusp prolapse into the defect, which can restrict the shunt but also cause aortic regurgitation; it’s best seen in parasternal long- and short-axis views at the base. Outlet defects almost never close spontaneously except by aortic valve prolapse.
• Malalignment VSD. With anterior deviation of the conal septum (as in tetralogy of Fallot), the septum is seen impinging on the RVOT from subxiphoid right anterior oblique and sagittal views, and out of line with the aorta, shifted anteriorly, on parasternal short-axis. In subtle malalignment without RVOT obstruction (an Eisenmenger-type VSD) the pulmonary artery is slightly larger than the aorta, whereas in tetralogy it’s usually smaller. With posterior deviation, hypoplasia of the aortic valve in association with a VSD is often the first clue: the aortic valve sits entirely over the LV and the conal septum appears to sit within the LV outflow on apical and parasternal long-axis views. Associated anomalies include a narrowed subaortic region, bicuspid aortic valve, and aortic arch obstruction or interruption (most commonly type B). See Tetralogy of Fallot for the anterior-malalignment picture.
• Muscular VSD. Often multiple, and because they’re surrounded by muscle and narrow in systole, small ones are hard to see on 2D — color Doppler greatly helps find them, though the jet must be seen to traverse the septum from one ventricle to the other. Multiple defects give a “Swiss cheese” septum. On parasternal short-axis from base to apex, posterior muscular defects appear between 7 and 10 o’clock, mid-muscular between 10 and 12, and anterior muscular between 12 and 3. Make sure the color box covers the most anterior and posterior septum. A subxiphoid short-axis sweep highlights the muscular septum, and apical sweeps show posterior, mid, and apical defects. Small muscular defects next to a larger VSD can be hard to see because there’s no pressure gradient across them, and are sometimes missed on preoperative imaging.

Physiologic Assessment

Direction of flow is determined by Doppler. Restriction is estimated from the peak velocity across the shunt — the higher the velocity, the higher the gradient across the defect and the lower the RV pressure. The Doppler beam should be as parallel to the VSD flow as possible to get the most accurate velocity. Because the velocity only gives one estimate of RV pressure, also estimate it from the tricuspid regurgitation velocity, the septal curvature at end-systole, RV size and hypertrophy, and RV function. The magnitude of the shunt and its effect on the left heart come from LA and LV size and LV systolic and diastolic function.

RV systolic pressure can be estimated directly from the peak VSD jet velocity using the modified Bernoulli equation — RVSP is approximately systemic systolic blood pressure minus 4 × (VSD peak velocity)². Qp:Qs is calculated, the same way as for an ASD, from Doppler stroke volumes at the RVOT/PA and LVOT: a ratio of 1:1 is normal, and ≥1.5:1 is the conventional threshold for a hemodynamically significant shunt.

Pitfalls: Real Defect or Artifact?

• A bright “T artifact” at the edge of a septal defect — echo-dense areas at the blood–tissue interface — helps confirm a true defect rather than the dropout that can otherwise mimic one.
• The membranous septum is particularly thin and produces dropout that can mimic a defect, so be careful interrogating it; aligning the septum perpendicular to the beam allows color Doppler to help find true defects.
• Septal flattening (“D-shaped” LV) specifically reflects elevated RV pressure — a marker of a large, poorly-restrictive VSD or of Eisenmenger physiology, rather than a routine finding in every VSD.

3D and Contrast Echocardiography

3D echocardiography enables en face visualization of the defect from both the RV and LV sides, showing its relationship to surrounding valves — including aortic valve prolapse through an outlet defect — which is useful for surgical and interventional planning and for defining margins for device closure. Contrast echocardiography has a narrower but real role: assessing residual shunting after surgical or device closure, and detecting right-to-left shunting once Eisenmenger physiology has developed.

How to Diagnose It: A Practical Sequence

1. Sweep the whole septum in more than one window — subxiphoid (long-axis, short-axis, left anterior oblique), apical (starting posteriorly at the coronary sinus), and parasternal (long-axis tilts and the base-to-apex short-axis sweep) — rather than stopping at the first defect found.
2. Use color Doppler throughout, with the color box covering the extreme anterior and posterior septum, and confirm the jet crosses from one ventricle to the other.
3. Classify by border and location: use the aortic-valve clock face on parasternal short-axis to separate perimembranous (about 9 to 12 o’clock, adjacent to the tricuspid valve) from outlet (about 12 to 2 o’clock), the presence or absence of a muscular rim to separate inlet perimembranous from posterior muscular, and the clock positions to place muscular defects (7–10 posterior, 10–12 mid, 12–3 anterior).
4. Look at the neighbors: is there fibrous continuity between valves, is the conal septum absent or malaligned, and is an aortic cusp prolapsing? Check for an RV muscle bundle and a subaortic membrane.
5. Count the defects — muscular VSDs are often multiple, and small ones can hide behind a large one.
6. Determine flow direction and restriction with a parallel Doppler beam, and estimate RV pressure from the VSD velocity, the TR jet, septal curvature, and RV hypertrophy.
7. Quantify the consequences: LA and LV size (as z-scores, over serial studies), LV function, and Qp:Qs.
8. Rule out artifact (T artifact, membranous septal dropout), and use TEE when transthoracic windows are inadequate.

Adults, Prenatal, and Intervention

• Adults. Imaging can be problematic because of body habitus and lung disease, yet adequate visualization is important for surveillance of associated lesions — aortic insufficiency with cusp prolapse, double-chambered RV, subaortic membrane, and progressive LV dilation, plus endocarditis. Eisenmenger syndrome typically presents in adolescence or early adulthood with reversed flow, elevated RV pressure, RV hypertrophy, and a flattened septum. TEE is useful when TTE is suboptimal, and in adults can often be done with moderate sedation rather than general anesthesia. See Eisenmenger Syndrome.
• Prenatal. VSD is hard to detect in the fetus: fetal movement limits image quality, and because right and left ventricular pressures are equal in utero, overlying tissue can obscure even a large conoventricular defect. In the four-chamber view with the beam parallel to the septum, the T artifact separates true VSDs from dropout; aligning the septum perpendicular to the beam lets color Doppler help, and decreasing the color scale helps detect low-velocity ventricular shunting. Trisomy 18 or 21 should raise suspicion.
• Transcatheter closure. TEE guides device placement, sizes the defect, and checks for residual defects or impingement on the AV or aortic valve on deployment; intracardiac echo is an alternative that can avoid general anesthesia in larger patients. Muscular defects, in particular, can be hard to close surgically because of dense RV trabeculations, so transcatheter approaches (femoral or hybrid perventricular) are valuable for them, and central perimembranous defects may be closed this way too.

Treatment Considerations

Closure criteria follow a structured, multi-parameter framework rather than a single number, and include special circumstances beyond shunt magnitude alone:

	Class I	Class IIA	Class IIB	Class III
LV volume overload	Present	—	—	—
Qp:Qs	>1.5:1 (net left-to-right)	—	>1.5:1 (net left-to-right)	Under 1.0 (net right-to-left)
PA pressure	Under 50% systemic	—	>50% systemic	>2/3 systemic
PVR	Under one-third systemic	—	>1/3 systemic	>2/3 systemic
VSD-related aortic regurgitation	—	Surgical closure reasonable for worsening AR from a perimembranous or supracristal VSD	—	—
VSD-related infective endocarditis	—	—	Surgical closure may be reasonable after IE caused by the VSD	—

Notice that worsening aortic regurgitation from a perimembranous or supracristal VSD is its own, independent indication for surgical closure — not something that only matters once shunt-based criteria are also met. Severe, irreversible pulmonary arterial hypertension remains the primary contraindication to closure.

• Surgical closure remains the classic approach, typically with a synthetic (or occasionally pericardial) patch, and is the default for perimembranous and doubly committed defects given their proximity to the conduction system and valves.
• Percutaneous closure is a real but genuinely narrower option than for ASD: congenital muscular VSDs away from the valves are the principal type amenable to device closure. Perimembranous and juxta-arterial defects are generally not suitable given their proximity to the conduction system and adjacent valve leaflets. Devices have also been used off-label for post-infarction muscular defects and for residual defects after prior surgical attempts.
• Many small muscular VSDs close spontaneously through growth or hypertrophy of the surrounding trabeculations; small outlet-type muscular defects can close through a similar mechanism, aortic valve leaflet prolapse into the defect, or fibrous deposition at the margins. Perimembranous and juxta-arterial defects are less likely to close spontaneously.
• Antibiotic prophylaxis for infective endocarditis is guideline-directed and considerably narrower than older teaching would suggest — society guidelines have moved away from routine prophylaxis for an isolated, uncomplicated VSD, reserving it for specific higher-risk situations (recent prosthetic material, a residual defect adjacent to prosthetic material, cyanotic unrepaired disease, or a prior episode of endocarditis, among others). Current, jurisdiction-specific society guidance should be consulted directly rather than relying on a blanket “small VSDs need prophylaxis” rule.

Postoperative Follow-Up

• Residual VSD is the most common postoperative finding, most often adjacent to the patch (“peripatch”). These typically shrink or close spontaneously, particularly if under 3 mm — closure is expected in roughly 65% within a year of repair. Reoperation or device closure is considered when a residual VSD is significant (generally Qp:Qs above 2:1).
• Residual intramural defects are a distinct, higher-risk finding — seen particularly with malalignment-type defects where the patch was anchored to RV trabeculations rather than the aortic annulus — and carry significantly higher morbidity and mortality than a simple peripatch defect, so distinguishing the two matters. On TEE they’re found by interrogating the most anterior portion of the ventricular septum, and unlike peripatch defects they’re less likely to close and can enlarge over time.
• Look for additional defects remote from the repair site — small ones can be hidden preoperatively by high RV pressure and limited ventricular-level shunting, and become more obvious after RV pressure falls. In large VSDs with systemic RV pressure beforehand, estimate RV pressure from the TR jet or residual VSD velocity to confirm it has normalized.
• Postoperative imaging (often TEE, performed after weaning from cardiopulmonary bypass) should also screen for tricuspid valve regurgitation or stenosis (from septal leaflet detachment/resuspension during exposure), aortic or pulmonary valve dysfunction (if a transvalvar surgical approach was used), and RV function (particularly after a ventriculotomy approach). LV function can be transiently reduced immediately after closure of a large VSD, from the abrupt increase in LV afterload once the low-resistance shunt path is removed.

Clinical Importance

Untreated large VSDs progress toward pulmonary vascular disease and Eisenmenger syndrome with irreversible cyanosis; VSD-related aortic regurgitation and infective endocarditis are each independent complications requiring their own management consideration rather than being purely downstream of shunt severity. See Atrial Septal Defect for the parallel shunt-lesion framework on the atrial side, Right Ventricle Evaluation for how resultant RV pressure and volume changes are assessed, and Aortic Regurgitation for the broader picture of AR mechanism and severity grading relevant to VSD-associated AR.