An aortopulmonary septal defect is a hole between the main artery that leaves the heart (aorta) and the artery that goes to the lungs (pulmonary artery). This extra shortcut sends too much blood to the lungs, so symptoms show up early and get louder fast.

Fast breathing is the first clue. Babies breathe more quickly than normal, especially during feeding or crying.

Poor weight gain follows. Infants tire at the bottle, take long pauses, and don’t add ounces like their peers.

Heart racing or pounding is common. You can feel the baby’s chest thumping when you pick them up, or notice a fast pulse in the neck.

Frequent chest infections pop up. The extra wet lung tissue makes a good landing spot for viruses.

A loud heart murmur is often heard early; it sounds like a washing machine between heartbeats.

Late signs include blue lips or fingernails during crying, swollen legs, or an enlarged liver—an alarm that the heart is working too hard.