This report presents a case of patent ductus arteriosus complicated with total left lung atelectasis and mitral regurgitation. Her mother complained growth retardation and exertional dyspnea. The 3 year old girl had large patent ductus arteriosus [Qp/Qs=5.6] which resulted in moderate pulmonary hypertension, left atrial hypertrophy and enlargement, consequently the left main bronchus was compressed between the dilated left atrium and aorta. We would like conclude the cause of mitral regurgitation as the result of annular dilatation secondary to left atrial enlargement rather than congenital associated to patent ductus arteriosus. 3 weeks later from ligation of patent ductus arteriosus, the left atrial dimension was markedly reduced echocardiographically [from 3.9cm to 2.7cm], and the left lung progressively aerated by halves.[KTCS 1978;3:316-320]