In two infants the anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) was detected prospectively by transoesophageal echocardiography (TEE). Colour flow mapping and pulsed Doppler ultrasound revealed a predominant right-to-left shunt from the pulmonary artery to the left coronary artery. These findings were confirmed by angiography. Transthoracic echocardiography (TTE) failed to show the anomalous origin of the left coronary artery or any abnormal pulmonary flow pattern. TEE may be useful in the diagnosis of ALCAPA in selected cases, when TTE is inconclusive.