# Ventricular Septal Defect and Patent Ductus Arteriosus

> VSD and patent ductus arteriosus for NEET-PG Medicine covering shunt murmurs, Maladie de Roger, the continuous machinery murmur and differential cyanosis.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/ventricular-septal-defect-and-patent-ductus-arteriosus
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Nelson Textbook of Pediatrics; Braunwald's Heart Disease; Harrison's Principles of Internal Medicine
- How to cite: "Ventricular Septal Defect and Patent Ductus Arteriosus", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/ventricular-septal-defect-and-patent-ductus-arteriosus

## Direct answer

Ventricular septal defect and patent ductus arteriosus are two common left-to-right shunts. A VSD produces a pansystolic murmur at the lower left sternal edge, while a PDA produces a continuous machinery murmur below the left clavicle. Shunt size drives management, and closure is indicated when the pulmonary to systemic flow ratio is about 1.5 or more with left ventricular volume overload. In both lesions the danger is pulmonary vascular disease, which can reverse the shunt and produce Eisenmenger physiology.

## What you must remember

- **VSD murmur:** pansystolic at the lower left sternal edge, often with a thrill; a small VSD is loud, while a large one can be soft because pressures equalise.
- **Maladie de Roger:** a small, usually isolated VSD with a loud murmur and normal heart size, with an excellent prognosis.
- **PDA murmur:** a continuous machinery murmur at the left infraclavicular area, with a wide pulse pressure and a bounding Corrigan pulse.
- **Shunt reversal:** when pulmonary resistance reaches systemic levels, the murmur disappears, cyanosis develops and P2 becomes loud.
- **Differential cyanosis:** cyanosed legs with pink arms in a PDA with reversed flow, because desaturated blood enters the descending aorta.
- **Closure:** surgical or device closure for VSD; transcatheter device closure for PDA, and indomethacin, ibuprofen or paracetamol in preterm neonates.
- **Differentials:** a venous hum disappears when the neck is compressed or the child lies flat; fistulas also produce continuous murmurs.
- **Endocarditis:** both lesions carry endocarditis risk, which guides prophylaxis per current guidance.

## Why a loud murmur can mean a small hole

A four-year-old boy is brought for a routine check with a loud pansystolic murmur and a thrill at the lower left sternal edge. He feels well, grows normally and has clear lungs.

1. **Assess the murmur:** The ventricles are not dilated, and the echo shows a small perimembranous defect.
2. **Name the lesion:** This is Maladie de Roger, in which a high-velocity jet crosses a steep pressure gradient. Management is reassurance, follow-up echo and endocarditis awareness.
3. **Contrast a large defect:** A one-year-old with a soft holosystolic murmur, poor feeding and an enlarged left heart has a large defect. Flow equalises ventricular pressures, reducing the turbulent gradient, so murmur loudness does not measure defect size.
4. **Time the closure:** Closure is planned before pulmonary vascular disease develops.
5. **Treat a preterm PDA:** A continuous murmur, wide pulse pressure and bounding pulse are treated with indomethacin or ibuprofen if the shunt is significant, with paracetamol in some centres. Surgical or transcatheter closure follows if medical therapy fails.
6. **Close older patients:** In older children and adults, transcatheter device closure is the usual route.

## Where the examiner tests the murmur

Four murmur traps recur in VSD and PDA questions.

- **Trap:** assuming a louder murmur means a bigger defect. — **Correct:** in VSD the opposite can be true, since a tiny defect with a steep gradient gives a harsh murmur while a large defect gives a softer one.
- **Trap:** attributing differential cyanosis to any PDA. — **Correct:** it belongs to a PDA with pulmonary hypertension and reversed flow, and a stem with lower limb cyanosis, pink arms and a loud P2 points to Eisenmenger physiology.
- **Trap:** choosing transcatheter closure for a preterm PDA. — **Correct:** a preterm infant calls for indomethacin or ibuprofen, while transcatheter closure is the usual route in older children and adults.
- **Trap:** treating every continuous murmur as a shunt. — **Correct:** the venous hum is continuous but disappears when the child lies flat or the jugular vein is compressed, and it signals no shunt.

## Frequently asked questions

### Why can a small VSD produce a louder murmur than a large one?

A small defect creates a high-velocity jet across a steep pressure gradient, producing a loud, harsh murmur. A large defect equalises ventricular pressures, so the murmur is softer despite the greater flow.

### What is the difference between a machinery murmur and a venous hum?

A patent ductus arteriosus produces a continuous machinery murmur, whereas a venous hum disappears when the neck is compressed or the child lies flat. The machinery murmur reflects a true shunt and needs investigation.

### What is Maladie de Roger?

Maladie de Roger is a small, usually isolated VSD with a loud murmur and normal heart size. It carries an excellent prognosis and needs reassurance and follow-up rather than surgery.

### Which drugs close a patent ductus arteriosus in preterm infants?

Indomethacin and ibuprofen are prostaglandin synthesis inhibitors used to close a patent ductus arteriosus in preterm neonates. Paracetamol is used in some centres as an alternative.

### What is differential cyanosis?

Differential cyanosis is cyanosis of the lower limbs with pink arms. It suggests a PDA with right-to-left flow, typically in pulmonary hypertension. The upper body is spared because the shunted blood enters the descending aorta after the arch vessels.