A 83 year old diabetic woman was admitted to our hospital with the diagnosis of subacute inferoposterior myocardial infarction. Four days later physical examination revealed a new systolic murmur at the left sternal border and apex. Transthoracic echocardiogram showed inferoposterior akinesis and a dissection tract in the posterior wall of the left ventricle arising from the distal to mid-segment with an entrance tear of 7 mm. Doppler color showed a systolic jet with a mosaic flow pattern inside the right atrium which appeared to originate in the coronary sinus. Transesophageal echocardiogram confirmed the intramyocardial dissection of the posterior wall and its communication with the coronary sinus, and identified the latter as the origin of the mosaic flow inside the right atrium. Medical treatment was initiated and the patient has been followed up for two years. The diameter of the entrance tear remains unchanged although the dissection tract and coronary sinus have enlarged, no significant enlargement has been observed in the right chamber on follow up.