A 65-year-old man with a postero-lateral myocardial infarction, complicated by rapid atrial fibrillation was admitted to the Intensive Coronary Care Unit. He received thrombolytic treatment. Electrocardiography and laboratory analysis were suggestive of reperfusion; the rapid atrial fibrillation was converted to sinus rhythm using i.v. amiodarone. Two echocardiograms performed on days 1 and 6 revealed hypokinesis of the postero-lateral wall and a mild reduction in the left ventricular ejection fraction. On day 7, after pharmacological wash-out, he was submitted to a bicycle exercise test: soon after the beginning of the 75 W step, the patient presented cardiac arrest due to electromechanical dissociation and hemopericardium. Despite prolonged cardiopulmonary resuscitation maneuvers and drainage of a few milliliters of pericardial blood, the patient did not survive. At autopsy, a huge clot filling the pericardial space was detected together with two linear 3 cm tears of the left ventricular lateral wall. The authors stress the possibility of unpredictable deaths during a pre-discharge exercise testing; good clinical judgment should therefore be used in deciding which patients should undergo this procedure and appropriate information about its potential risks should be given.