What is Left-to-Right Shunt Congenital Heart Disease?

Left-to-right shunt congenital heart diseases are among the most commonly diagnosed heart defects in clinical settings. These conditions include atrial septal defect (ASD), ventricular septal defect (VSD), and patent ductus arteriosus (PDA). In a normal heart, oxygen-rich (arterial) blood is separated from oxygen-poor (venous) blood. However, in left-to-right shunt defects, there is an abnormal communication that allows arterial blood to flow into the venous circulation, increasing the workload on the heart and lungs.

Understanding Left-to-Right Shunts

Left refers to the arterial side of the circulatory system, while right refers to the venous side. A left-to-right shunt means that oxygenated blood from the left side of the heart flows abnormally into the right side, which carries deoxygenated blood. This results in increased blood flow to the lungs and can lead to complications such as pulmonary hypertension if left untreated.

Atrial Septal Defect (ASD)

ASD is a condition where there is a hole in the wall (septum) that separates the two upper chambers of the heart — the left and right atria. As a result, oxygen-rich blood from the left atrium flows into the right atrium, mixing with deoxygenated blood. This extra volume of blood increases the workload on the right side of the heart and the pulmonary circulation.

Ventricular Septal Defect (VSD)

VSD is characterized by a hole in the septum between the left and right ventricles — the lower chambers of the heart. Oxygenated blood from the left ventricle flows through the defect into the right ventricle, causing increased pulmonary blood flow. VSDs vary in size and severity, with larger defects often requiring surgical or catheter-based intervention to prevent long-term complications.

Patent Ductus Arteriosus (PDA)

In PDA, a blood vessel called the ductus arteriosus, which normally closes shortly after birth, remains open. This allows blood from the aorta (oxygenated) to flow into the pulmonary artery (which carries deoxygenated blood to the lungs). This abnormal shunting increases pulmonary blood flow and can lead to heart failure or developmental delays in infants if not treated.