ObjectiveTo study the action potential of sinoatrial node cells, atrial cells, and ventricular cells of neonatal rat.MethodsSinoatrial node cells, atrial cells, and ventricular cells were isolated and cultured by “enzymolysis with differential attachment” method from 12 neonatal Wistar rats within 24 hours.Whole-cell patch clamp technique was used to record the action potential of the three kinds of myocytes.ResultsSinoatrial node cells were small and slim with a spindle shape and frequencies at (152.1±10.9) beats/min.The atrial cells also had small body with nearly spindle like or triangular shape, and with the beating rate of (116.3±8.6) beats/min.The ventricular cells had large body, multi-stretch pseudopodia, and the shapes of short spindle, polygonal, or irregular shape.The beating rates of which were (92.4±9.3) beats/min. Significant difference in beating rates was observed among three kinds of cells (P＜0.01).The resting potential of the three kinds of cells were (-41.3±4.0) mV, (-50.7±2.9) mV, and (-59.8±2.1) mV, respectively, with no significant difference (P＞0.05).APD20, APD50, and APD90 in ventricular cells were longer than those in atrial cells and there were statistical differences (P＞0.05).ConclusionsThree kinds of cells are different in shape.Sinoatrial node cells have spontaneous pulsatility. The action potential duration of ventricular cells is longer than that of atrial cells.