Confusable diagnoses · PANCE / PANRE

Patent Ductus Arteriosus vs Ventricular Septal Defect

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

Patent Ductus Arteriosus 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.

Patent Ductus Arteriosus vs Ventricular Septal Defect at a glance

  • Patent Ductus Arteriosus: Persistent fetal connection between aorta and pulmonary artery producing a continuous machinery murmur and L-to-R shunt.
  • 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 Patent Ductus Arteriosus vs Ventricular Septal Defect

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Question 1CardiovascularEasy
A 6-week-old term girl is brought in for poor weight gain. Her mother reports she tires and sweats during feeds and breathes rapidly. On exam she is tachypneic with a hyperdynamic precordium, bounding peripheral pulses, and a wide pulse pressure. A continuous "machinery" murmur is best heard at the left infraclavicular area, peaking around the second heart sound. Which of the following is the most appropriate next diagnostic test to confirm the diagnosis?
  • ATransthoracic echocardiography, Doppler
  • BTwo-view plain chest radiograph series
  • CCardiac catheterization with angiography
  • DTwelve-lead surface electrocardiography
Reveal answer & full explanation
Correct answer: A — Transthoracic echocardiography, Doppler
  • ATransthoracic echocardiography, Doppler✓
  • BTwo-view plain chest radiograph series
  • CCardiac catheterization with angiography
  • DTwelve-lead surface electrocardiography

Why Transthoracic echocardiography, Doppler is correct

  • The continuous machinery murmur at the left infraclavicular area with bounding pulses and a wide pulse pressure is classic for a patent ductus arteriosus (PDA).
  • Echocardiography with color Doppler is the diagnostic study of choice: it directly visualizes the ductus, shows the direction and velocity of the shunt, and quantifies left atrial and left ventricular enlargement from chronic volume overload.
  • It is noninvasive, available at the bedside, and confirms the anatomic lesion.

Why the others are wrong

  • Two-view plain chest radiograph series may show cardiomegaly and prominent pulmonary vascularity in a moderate-to-large shunt, but these findings are nonspecific and cannot distinguish a PDA from other left-to-right shunts.
  • Twelve-lead surface electrocardiography can reveal left atrial enlargement and LVH with a large shunt, but it is normal with small defects and never identifies the anatomic lesion.
  • Cardiac catheterization with angiography is invasive and reserved for measuring pulmonary vascular resistance when pulmonary hypertension is suspected before closure, not for initial confirmation of the diagnosis.
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

FeaturePatent Ductus ArteriosusVentricular Septal Defect
At a glancePersistent fetal connection between aorta and pulmonary artery producing a continuous machinery murmur and L-to-R shunt.Opening in the interventricular septum causing a left-to-right shunt with a harsh holosystolic murmur at the LLSB.
Classic presentationContinuous machinery murmur with wide pulse pressure and bounding pulses in a child; differential cyanosis is pathognomonic when shunt reversal develops.; Small PDA: asymptomatic, found incidentally on auscultation; Moderate-to-large PDA in infancy: poor feeding, diaphoresis with feeds, failure to thrive, tachypnea, recurrent pulmonary…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 labsBMP, CBC; Genetic evaluation if features suggest a syndrome (Down, rubella exposure history)Basic labs are typically normal; BNP if HF symptoms
ImagingTransthoracic echocardiography with color Doppler — diagnostic; visualizes the ductus, direction and velocity of shunt, and chamber size; ECG: normal if small; LA enlargement and LVH with large shunts; biventricular hypertrophy with pulmonary HTN; CXR: cardiomegaly, prominent pulmonary vasculature, dilated proximal pulmonary arteries in…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 treatmentPremature infants: expectant management for most PDAs in the first 2 weeks (many close spontaneously), since prophylactic or early medical closure has not improved outcomes. Persistent hemodynamically significant PDA: pharmacologic closure with a COX inhibitor (ibuprofen or indomethacin) or acetaminophen; if unsuccessful, transcatheter…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

Patent Ductus Arteriosus (PDA) 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.