Ischemia causes a depression in myocardial activity and a deterioration in calcium homeostasis. This study was designed to investigate the protective effect of chlorpromazine, an inhibitor of phospholipase, on myocardial cells from ischemia or reoxygenation injury. Isolated hearts from Sprague-Dawley rats(200~230g BW) were suspended on the Langendorff's heart preparation apparatus. The myocardial activity was measured by means of left ventricular pressure(LVP), myocardial contractility(dp/dt) and heart rate(HR). Chlorpromazine 500ng/L did not affect the reduction of myocardial activity during global ischemia. In the period of reoxygenation, chlorpromazine, by the same concentration, strikingly increased the recovery of LVP and dp/dt while it did not affect the recovery of HR. These results suggest that chlorpromazine protects the myocardium from the reoxygenation injury.