In this study, Iigation of the anterior descending branch of the left coronary artery was used to produce acute myocardial ischemia in rats. Radioimmunoassay was performed to determine the dynamic changes of immunoreactive arginine vasopressin (ir-AVP) content after ischemia. Results showed that levels of ir-AVP of the plasma, some brain areas, pituitary and myocardium were markedly increased post-ischemia. Meanwhile the left ventricular myocardial contractility parameters such as dp/dtmax, ventricular systolic pressure and blood pressure were markedly decreased. Intravenous injection of anti-AVP serum 30 min before ligation could improve the function of the heart. Under light microscope, there were slight congestion and focal bleeding in the myocardial mesenchyma 2 h after coronary ligation and these changes were minimized or vanished with the use of anti-AVP serum before coronary Iigation.