We present the case of a 79-year-old man suffering from chronic atrial fibrillation, severe left ventricular dysfunction, massive right atrial thrombosis, and pulmonary hypertension. Complete coronary sinus thrombosis was found incidentally during preoperative screening. Successful coronary sinus, right atrial, and pulmonary operative embolectomy was followed soon after by a dramatic improvement of cardiac performance; the patient's left ventricular function recovery, in particular, suggests that cardiac venous system played an important role in the genesis of myocardial impairment.