Complete transposition of the great arteries (TGA) means the two main heart vessels are wired backward: oxygen-poor blood keeps circling to the body and oxygen-rich blood to the lungs. The mix-up is total, so symptoms start within hours of birth 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.

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.