Confusable diagnoses · PANCE / PANRE

Atrial Septal Defect vs Ventricular Septal Defect

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Atrial Septal Defect and Ventricular Septal Defect are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Atrial Septal Defect vs Ventricular Septal Defect at a glance

  • Atrial Septal Defect: Opening in the interatrial septum producing left-to-right shunt, fixed split S2, and risk of paradoxical embolism.
  • Ventricular Septal Defect: Opening in the interventricular septum causing a left-to-right shunt with a harsh holosystolic murmur at the LLSB.

Try two board-style questions on Atrial Septal Defect vs Ventricular Septal Defect

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Question 1CardiovascularMedium
A 44-year-old woman presents with several months of progressive exertional dyspnea and intermittent palpitations. She reports no prior cardiac history. Vital signs are normal. On auscultation there is a soft mid-systolic ejection murmur at the upper left sternal border and wide splitting of S2 that does not vary with respiration. A right ventricular heave is palpable at the lower left sternal border. ECG shows an incomplete right bundle branch block with right axis deviation, and chest radiograph reveals an enlarged right atrium and right ventricle with increased pulmonary vascular markings. Which of the following is the most likely diagnosis?
  • APulmonary valve stenosis
  • BVentricular septal defect
  • CSecundum atrial defect
  • DPatent ductus arteriosus
Reveal answer & full explanation
Correct answer: C — Secundum atrial defect
  • APulmonary valve stenosis
  • BVentricular septal defect
  • CSecundum atrial defect✓
  • DPatent ductus arteriosus

Why Secundum atrial defect is correct

  • Wide and fixed splitting of S2 that does not vary with respiration is the auscultatory hallmark of an atrial septal defect; the left-to-right shunt augments right atrial volume so right ventricular ejection time stays prolonged in both inspiration and expiration.
  • The soft pulmonic flow murmur (from increased flow across the pulmonic valve), the right ventricular heave, and right heart enlargement with increased pulmonary vascular markings all reflect chronic right-sided volume overload from the shunt.
  • An atrial septal defect is the most common congenital heart defect first diagnosed in adulthood, classically in a middle-aged woman presenting with dyspnea, palpitations or atrial arrhythmia, or unexplained right heart enlargement.
  • An ECG with incomplete right bundle branch block and right axis deviation is typical of the secundum subtype, which accounts for roughly 75% of atrial septal defects.

Why the others are wrong

  • Ventricular septal defect produces a holosystolic murmur at the lower left sternal border with a normally splitting S2, not a wide fixed split; large defects typically cause pulmonary congestion and heart failure in infancy rather than first presenting in adulthood.
  • Patent ductus arteriosus produces a continuous machinery murmur with a wide pulse pressure and bounding pulses, none of which are present here.
  • Pulmonary valve stenosis gives a systolic ejection murmur at the upper left sternal border with an ejection click; significant stenosis delays and softens P2, so the split S2 is wide but still varies with respiration. It is an isolated valvular lesion and does not produce a fixed split S2 or a left-to-right shunt with right heart volume overload.
Question 2CardiovascularMedium
A 68-year-old woman is recovering in the hospital on day 4 after an anterior ST-elevation myocardial infarction treated with stenting. She becomes acutely hypotensive and dyspneic. On examination she has a new harsh holosystolic murmur with a palpable thrill at the left lower sternal border, jugular venous distention, and pulmonary crackles. Blood pressure is 82/54 mm Hg and heart rate is 118/min. Which of the following is the most appropriate next diagnostic test?
  • ARight heart catheterization with oximetry
  • BTransthoracic echocardiography with Doppler
  • CCardiac MRI for shunt fraction quantification
  • DCoronary angiography with left ventriculography
Reveal answer & full explanation
Correct answer: B — Transthoracic echocardiography with Doppler
  • ARight heart catheterization with oximetry
  • BTransthoracic echocardiography with Doppler✓
  • CCardiac MRI for shunt fraction quantification
  • DCoronary angiography with left ventriculography

Why Transthoracic echocardiography with Doppler is correct

  • A new harsh holosystolic murmur with a thrill at the LLSB plus hemodynamic deterioration 3-7 days after MI is the classic presentation of post-infarction ventricular septal rupture.
  • Bedside transthoracic echo with color Doppler is the immediate test of choice: it directly visualizes the septal defect, demonstrates the left-to-right shunt jet, and assesses RV size and function to guide urgent surgical or transcatheter repair.
  • It is fast, portable, and noninvasive, making it ideal for an unstable patient in cardiogenic shock.

Why the others are wrong

  • Right heart catheterization with oximetry can confirm a shunt by detecting an oxygen step-up in the RV, but it is invasive and slower than echo, which has become the diagnostic standard for septal rupture.
  • Cardiac MRI for shunt fraction quantification accurately quantifies shunt fraction and complex anatomy in stable patients, but it is too slow and impractical for a hemodynamically unstable patient.
  • Coronary angiography with left ventriculography defines coronary anatomy before surgical repair, but it does not establish the mechanical diagnosis driving the acute decompensation and is not the first study for a new murmur with shock.
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Side-by-side comparison

FeatureAtrial Septal DefectVentricular Septal Defect
At a glanceOpening in the interatrial septum producing left-to-right shunt, fixed split S2, and risk of paradoxical embolism.Opening in the interventricular septum causing a left-to-right shunt with a harsh holosystolic murmur at the LLSB.
Classic presentationWide and fixed split S2 with pulmonic flow murmur in an otherwise asymptomatic adult.; Often asymptomatic in childhood; diagnosed in adulthood after decades of right heart volume overload; Exertional dyspnea, fatigue, palpitations (atrial arrhythmias); Recurrent respiratory infections in larger defects; Cryptogenic stroke or TIA…Harsh, blowing holosystolic murmur with palpable thrill at the LLSB; intensity inversely related to defect size in many cases.; Small VSD: asymptomatic, identified by murmur on routine examination; Moderate-to-large VSD in infancy: poor feeding, diaphoresis with feeds, failure to thrive, tachypnea, recurrent pulmonary infections, signs…
Workup / key labsHemodynamically significant ASD warranting closure: right heart (RA/RV) enlargement on imaging with Qp/Qs ≥1.5, without severe pulmonary hypertension. Closure may also be considered after documented paradoxical embolism or for platypnea-orthodeoxia. Closure is generally contraindicated if pulmonary vascular resistance is severely…Basic labs are typically normal; BNP if HF symptoms
ImagingTransthoracic echocardiography with agitated saline (bubble study) and color Doppler — visualizes defect, direction and magnitude of shunt, RA/RV size, RV function, and estimates pulmonary pressures; Transesophageal echocardiography for better characterization of sinus venosus and sinus coronarius defects and to evaluate suitability for…Transthoracic echocardiography with color Doppler — diagnostic; defines anatomy, size, shunt direction, chamber size, RV pressure, presence of AR (especially outlet VSD) or AV valve abnormalities; ECG: normal in small VSDs; LA enlargement and LVH with moderate-to-large shunts; biventricular hypertrophy with significant pulmonary HTN;…
First-line treatmentSecundum ASD: percutaneous transcatheter device closure (e.g., Amplatzer septal occluder) is the preferred approach when anatomy is suitable (adequate rims, defect <38 mm); Primum, sinus venosus, and unroofed coronary sinus defects, as well as secundum defects with inadequate rims: surgical patch closure; Antiplatelet therapy for about…Small, restrictive, asymptomatic VSD: observation; spontaneous closure is common in muscular and small perimembranous defects; Hemodynamically significant VSD (HF symptoms, growth failure, pulmonary hypertension reversible): surgical patch closure is the standard, typically in infancy or early childhood; Selected muscular VSDs may be…

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Full outlines

Atrial Septal Defect (ASD) Ventricular Septal Defect (VSD) All 514 diagnoses

Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.