Experiments were performed on 15 rabbits anesthetized with sodium pentobarbital.A contactelectrxxie was used to recond monophasic action potential(MAP)of endocardium of the right ventricle and a surfaceelectrode for electrocardiogram(ECC).Acute cardiac tamponade was made by injection of warm saline into thepericardial cavity.The resdts were as follows:there were no marked changes in QRS amplitude

the heart rate and thedifferent indices of MAP when small amount of saline(< 4ml)was injected.If the volume of saline injection increasedto 6ml

the amplitude of MAP(MAPA)started to lower asuIts indicated that MAP duration at 50% repolariation(MAPO50)prulorlged about 13.6ms(P<0.01)QRS ampliiude fell about 0.3mv(P<0.01)and the heart mte decreasedto 54 beats/min(P< 0.01)All the above criteria changed more obviously as the volume of saline injection increasedto more than 10ml. It is suaested that besides the diastolic filling of the ventricle of myocardial cell was also affected.The activityof the ionic channel or ionic pumps of the heart muscle cells may be affceted by acute cardiac tamponade. Thisproblem should be cousidelxld when acute tamponade is treated clinically.