**Question:** An young man previously diagnosed as a case of congenital! hea disease-left to right shunt has a very loud pansystolic murmur at the left sternal edge without any hemodynamic disturbance. He is likely to be having-

A. Patent Ductus Arteriosus (PDA)
B. Atrial Septal Defect (ASD)
C. Ventricular Septal Defect (VSD)
D. Pulmonary Stenosis (PS)

**Correct Answer:**

**Core Concept:** Congenital heart diseases with left to right shunt can present with a pansystolic murmur at the left sternal edge, which is a result of the increased blood flow through the shunt causing turbulence and turbulence-induced valvular regurgitation.

**Why the Correct Answer is Right:**

The correct answer, Patent Ductus Arteriosus (PDA), is a congenital heart defect characterized by the persistence of the fetal ductus arteriosus, which normally closes shortly after birth. PDA allows blood to bypass the lungs and flow directly from the aorta to the pulmonary artery, causing left to right shunting. This results in a pansystolic murmur at the left sternal edge due to turbulence and turbulence-induced valvular regurgitation.

**Why Each Wrong Option is Incorrect:**

A. Atrial Septal Defect (ASD) is a congenital heart defect involving a hole in the interatrial septum, allowing oxygenated blood to mix with deoxygenated blood, leading to a decrease in oxygen saturation. An ASD does not result in left to right shunting, so it would not present with a left sternal edge murmur.

B. Atrial Septal Defect (ASD) is a congenital heart defect involving a hole in the interatrial septum, allowing oxygenated blood to mix with deoxygenated blood, leading to a decrease in oxygen saturation. An ASD does not result in left to right shunting, so it would not present with a left sternal edge murmur.

C. Ventricular Septal Defect (VSD) is a congenital heart defect involving a hole in the ventricular septum, allowing oxygenated blood to mix with deoxygenated blood, leading to a decrease in oxygen saturation. A VSD does not result in left to right shunting, so it would not present with a left sternal edge murmur.

D. Pulmonary Stenosis (PS) is a congenital heart defect where there is narrowing of the pulmonary artery, restricting blood flow to the lungs, leading to increased pulmonary vascular resistance and decreased oxygen saturation. PS results in right to left shunting, not left to right shunting, and would not present with a left sternal edge murmur.

**Clinical Pearl:**

In congenital heart diseases, the relationship between the type of defect, the direction of shunting, and the location of the murmur are crucial for accurate diagnosis. A left sternal edge murmur is indicative of a left to right shunt, which is associated with PDA, ASD, or VSD. In contrast, right to