Abnormal small fistulous flows in the pulmonary artery were detected on routine transthoracic echocardiography in asymptomatic patients by colour Doppler echocardiography. The most likely diagnosis is small coronary artery-pulmonary artery fistulas. We evaluated the clinical, echocardiographic, and follow-up findings of 101 patients. The mean age at first echocardiographic evaluation was 4.3 +/- 4.2 years. In 79 (78.2%) of the patients, fistula flow in the pulmonary artery was diagnosed at the first presentation and the remaining 22 patients (21.8%) were diagnosed between the 2nd and 10th examination. The echocardiography indication was cardiac murmur in 42 (41.6%), routine cardiac control in 30 (29.7%), additional CHD in 14 (13.8%), non-specific chest pain in 11 (10.9%), suspicion of inflammatory heart disease in 2 (2%), and syncope in 2 (2%) patients. In 70 (69.3%) patients, fistulous flow was located in the anterior aspect of the main pulmonary artery, in 23 (22.8%) patients on the aortic side of the pulmonary artery and in 8 (7.9%) patients on the right pulmonary artery. Additional cardiac anomalies were ventricular septal defect in 8, patent ductus arteriosus in 6, atrial septal defect in 5, mitral valve prolapse in 4, coarctation of aorta in 4, bicuspid aortic valve in 3, and Kawasaki syndrome in 1 patient. Sixty-four patients (63.3%) were followed during a mean of 52.6 +/- 43.7 months. Spontaneous closure was detected in only three patients; the others remained almost unchanged during the follow-up. Since the fistulas are thin and hemodynamically insignificant, echocardiography is an appropriate method to monitor these patients without performing any invasive diagnostic procedures for the fistula source.