During a routine medical check-up, a pathological electrocardiogram was recorded in an asymptomatic 6 year old girl. The demonstration of coronary insufficiency by exercise stress testing and sestamib myocardio-scintigraphy led to the diagnosis of an anomalous origin of the left coronary artery. This vessel arose from the right coronary sinus and continued anteriorly to the main coronary artery. The data of the literature suggest that the risk of sudden death and of coronary insufficiency is associated with the passage of the left coronary artery between the aorta and pulmonary artery. The authors describe the anomalous origin of the left coronary artery and its trajectory with respect to the great vessels by echocardiography, using a high frequency transducer. The anterior direction of the left coronary artery in front of the main pulmonary artery may lead to ischaemia on effort even without stenosis at coronary angiography. Echocardiography may therefore be useful in children with positive exercise stress tests for diagnosing anomalous coronary vessels and their relationship with respect to the great vessels.