The ability to differentiate Intraoperatively between myocardial stunning, which Is reversible, and Irreversible myocardial Infarction has major Implications because It provides a rational approach to the use or withholding of ventricular assist devices In patients with severe postcardlotomy ventricular dysfunction. Two Illustrative cases are presented. (J Card Surg 1994;9[Suppl]:403-409)