How can a heart septal defect change the flow of blood through the heart and lungs?

A heart septal defect creates an abnormal opening in the partition between the heart's chambers, which alters blood flow by allowing blood to "short circuit" between the left and right sides of the heart.1

In a typical septal defect, blood is shunted from the left side of the heart to the right, leading to an increased volume of blood entering the pulmonary circulation. This forces the heart to pump more blood through the lungs than through the rest of the body. Over time, this excessive flow and volume can cause:231

• Pulmonary Hypertension: Increased blood pressure within the lungs, which may lead to irreversible damage to the pulmonary artery walls.213
• Right Heart Strain: The right ventricle must work harder to manage the increased volume, potentially leading to right heart failure.13
• Oxygenation Issues: The abnormal mixing of oxygenated and deoxygenated blood can compromise the supply of oxygen to body tissues.1

In complex conditions like tetralogy of Fallot, the flow can reverse, shunting deoxygenated blood into the systemic circulation and causing cyanosis.21