Atrial Septal Defect

An atrial septal defect is an opening in the wall that normally separates the two upper chambers of the heart. In a healthy heart, this wall keeps oxygen-rich blood on the left side separate from oxygen-poor blood returning from the body on the right. When an opening exists, blood can flow between these chambers in ways it ordinarily would not, and over time this can alter how the heart and lungs work. Many dogs and cats with small openings show no outward signs, and the condition may be discovered during a routine examination when a heart murmur is heard. Others may develop reduced stamina, breathe more rapidly than usual during rest, or show a reluctance to exercise as they grow. The pattern depends largely on the size of the opening and how much blood is crossing between the chambers. This page explores the signs that may bring an atrial septal defect to attention, the mechanisms by which an opening affects circulation and heart structure, the investigations used to confirm and characterise it, and the range of approaches that exist for managing it across a dog or cat's life.