Abstract: AIM To observe the effects of ethanol at different concentrations on electric-physiological characteristics of isolated guinea pig myocardium. METHODS Standard microelectrode technique was used to record the action potentials (AP) of isolated guinea pig myocardium and the variations of 12.5, 25.0, 50.0, 100.0 and 200.0 mmol/L ethanol on AP parameters in atrium and papillary were analyzed. RESULTS Resting membrane potential (RMP), action potential amplitude (APA), action potential duration (APD), action potential duration of 50% repolarization (APD50) and action potential duration of 90% repolarization (APD90) in isolated papillary were not affected with 12.5-100.0 mmol/L ethanol but APA decreased with 200 mmol/L（P<0.05）. APD, APD50 and APD90 in isolated atrium were significantly prolonged with 50.0-200.0 mmol/L ethanol （P<0.05 or P<0.01） and APA was reduced with 200 mmol/L （P<0.05）. CONCLUSION Ethanol at different concentrations has significant different effect on electric-physiological characteristics of isolated guinea pig myocardium. The prolonged effect of APD on atrium may be related to the inhibition of special ion channels.