A 70-year-old woman underwent an aortocoronary bypass. Three hours later, she experienced severe pulmonary embolism, diagnosed by transesophageal echocardiography and followed by cardiac arrest. Resuscitation maneuvers were unsuccessful. Autopsy confirmed the diagnosis. When pulmonary embolism occurs after cardiopulmonary bypass for cardiac surgery, it usually occurs in the 2nd postoperative week; and to the best of our knowledge, the literature contains no other reports of cases that occurred during a shorter postoperative interval. Prevention of pulmonary embolism in high-risk patients is mandatory. When embolism occurs, transesophageal echocardiography is an essential tool in making the diagnosis and in guiding the surgeon during intervention.