Thrombus at ostium of coronary sinus discovered during evaluation for cardiac resynchronization therapy.

A 50-year-old male patient with dilated cardiomyopathy was evaluated for cardiac resynchronization therapy. A transthoracic echocardiogram revealed a mass in close proximity to the coronary sinus ostium.The mass was considered to be a thrombus and found to have disappeared at the repeat echocardiogram performed following a month of anticoagulation therapy with warfarin. In this case report, we aim to emphasize the importance of coronary sinus imaging, especially during echocardiographic evaluation for cardiac asynchrony.