Objective: To observe the effects of metoprolol tartrate on permanent heart pacing threshold and endocardial electrical signal amplitude. Methods: 57 patients who had been implanted pacemaker one to three days were observed, among them, 43 patients received implanting new pacemaker and 14 patients received replacing pacemaker. Metoprolol tartrate 10mg (weight0.05). It also doesn't affect any pacing threshold parameter of the patients who had been replaced pacemaker significantly (p>0.05).