**Core Concept**
Total anomalous pulmonary venous connection (TAPVC) is a congenital heart defect characterized by the abnormal connection of the pulmonary veins to the right atrium, coronary sinus, or other systemic veins, leading to oxygenated blood returning to the right side of the heart instead of the left. This results in a left-to-right shunt, causing increased pulmonary blood flow and potential for pulmonary congestion.

**Why the Correct Answer is Right**
In TAPVC, the pulmonary veins are connected to the right atrium or its tributaries, bypassing the left atrium. This abnormal connection prevents oxygenated blood from reaching the left ventricle, leading to decreased systemic oxygenation and potential cyanosis. The most common type of TAPVC is supracardiac, where the pulmonary veins connect to the superior vena cava or its tributaries.

**Why Each Wrong Option is Incorrect**
**Option A:** TAPVC is commonly associated with a left-to-right shunt, which is incorrect because it is actually a classic cyanotic congenital heart defect.
**Option B:** The most common type of TAPVC is infradiaphragmatic, which is incorrect because supracardiac is the most common type.
**Option C:** TAPVC is often asymptomatic at birth, which is incorrect because most infants with TAPVC present with symptoms such as respiratory distress, failure to thrive, and cyanosis.

**Clinical Pearl / High-Yield Fact**
TAPVC is often associated with other congenital heart defects, such as atrial septal defects or ventricular septal defects, and can be diagnosed prenatally using echocardiography.

**Correct Answer: B. Infradiaphragmatic is the least common type of TAPVC.**