Complete atrioventricular septal defect (CAVSD) is a large hole in the center of the heart combined with one shared valve instead of two separate ones. Blood swirls in the wrong directions, so symptoms start early and snowball fast.

Blue color is the first clue. Lips, tongue, fingers, and toes look dusky or deep purple, especially when the baby cries or feeds.

Fast, labored breathing is constant. The infant uses more breaths per minute and may grunt with each exhale.

Poor feeding and sweating appear early. Babies tire at the bottle, fall asleep quickly, and bead sweat on the forehead.

Heart murmur is loud. A washing-machine sound is heard even without a stethoscope.

Weak or absent pulses can show in the legs if the ductus is closing.

Sudden collapse can happen when the temporary fetal vessel (ductus arteriosus) closes—an emergency that needs immediate surgery.