Ramkumar a 70 year old hypeensive male was admitted in the intensive care unit with transmural anterolateral myocardial infraction. His condition was stable till fifth day of admission, when he developed a pericardial friction rub and pleuritic chest pain which persisted despite narcotic and steroid therapy. On the seventh morning, he suddenly developed marked hypotension. On examination there was marked distension of the jugular veins, accompanied with electromechanical dissociation. Most likely, the patient had developed :