Naloxone blocks the cardiac effects of myocardial ischaemia and reperfusion in the rat isolated heart.

The effects of naloxone on contractility and cardiac rhythm were studied in the rat isolated perfused heart during myocardial ischaemia and reperfusion. Pretreatment of the rat isolated perfused heart with naloxone abolished the reduction in left ventricular pressures and attenuated greatly the arrhythmias due to myocardial ischaemia and reperfusion. Administration of naloxone into the fibrillating rat isolated heart induced by myocardial ischaemia and reperfusion also attenuated the arrhythmias in a dose-dependent manner. The results indicate a possible involvement of the endogenous opioid peptides in the cardiac effects due to myocardial ischaemia and reperfusion. The antiarrhythmic effect of naloxone has great clinical implications.