Coronary sinus (CS) thrombosis is a rare event, usually complicating invasive procedures that cause trauma to the CS. Based on anecdotal case reports, this pathology is frequently associated with serious complications and is commonly fatal. We describe a case of intermittent CS thrombosis resulting from CS cannulation during coronary artery bypass grafting operation. This complication was further complicated by myocardial infarction, left ventricular free wall rupture, and pseudoaneurysm formation. The characteristic echocardiographic findings and a review of the literature on this rare complication are presented.