AIM: The aim of this study was to study the changes of rabbit heart electrophysiological properties caused by increasing left ventricular afterload, and to assess the effects of streptomycin or verapamil on these changes. METHODS: The rabbit heart preparation in situ was used,and the afterload of left ventricle was increased by clipping in part the root of ascending aorta. The changes of heart electrophysiological parameters including relative refractory period (RRP),effective refractory period (ERP),monophasic action potential duration (MAPD_ 90 ) and ventricular fibrillation threshold(VFT) were observed before and after altering the afterload of left ventricle and were compared in the absence and presence of streptomycin or verapamil. RESULTS: The rising of left ventricular afterload [(72?11)mmHg] led to shortening of RRP,ERP and MAPD_ 90 ,and to descent of VFT ( P 0.05) except increasing of VFT ( P