What is the most common heart defect characterized by left to right shunting of blood?

The most common heart defect characterized by left to right shunting of blood is a ventricular septal defect. In this condition, there is an abnormal opening in the septum that separates the left and right ventricles of the heart. This opening allows oxygen-rich blood from the left ventricle to flow into the right ventricle, which then gets pumped back to the lungs instead of out to the body. This left-to-right shunt leads to increased blood flow in the lungs, which can cause pulmonary hypertension and other complications if left untreated.

Ventricular septal defects are prevalent among congenital heart defects and can vary in size, which affects the severity of symptoms. Small defects may be asymptomatic, while larger defects can lead to significant clinical issues requiring intervention. In contrast, the other options listed also involve some form of shunting or obstruction, but ventricular septal defects are particularly noted for their prevalence and the characteristic left to right shunting they involve.