Aortopulmonary window (APW) is a rare heart defect that is present at birth. Children with APW have a hole connecting the major blood vessel that delivers oxygen-rich blood to the body (the aorta) and the one taking blood from the heart to the lungs to be oxygenated (pulmonary artery). This results in too much blood flowing to the lungs instead of to the body. This can increase blood pressure in the lungs, often causing rapid breathing and infections of the lungs. Other symptoms include delayed growth, failure of the heart to function properly, lack of weight gain and poor eating, and irritability. A doctor can diagnose APW by inserting a tube into the body and to the lungs to measure the pressure there. He or she can also diagnose APW with a chest exam and an imaging test called an echocardiogram. A cardiologist, or heart doctor, can work with you to determine the best treatment for this condition.