Naloxone inhibits early arrhythmias resulting from acute coronary ligation.

The intravenous administration of naloxone 15 min before acute coronary artery ligation in both anesthetized and conscious male rats markedly reduced the incidence and severity of the ventricular arrhythmias that occur within 30 min of the onset of myocardial ischaemia. The incidence of ventricular fibrillation was especially reduced and, in conscious rats, the survival 16 h after ligation was increased from 27% (in the controls) to 58 and 73% after 2 and 4 mg/kg naloxone respectively. One possible explanation of these results implies a detrimental effect of released endorphin in the early stages of myocardial ischaemia.