One hundred twenty-four patients with unipolar permanent pacemaker implantation (advanced atrioventricular block, 62 cases; sick sinus syndrome, 51 cases; and atrial fibrillation with slow ventricular response, 11 cases) were studied by 24-hour Holter electrocardiography. Analysis of pacemaker function and arrhythmias with various pacing modes (VVI pacing, 70 cases; AAI pacing, 19 cases; and DDD pacing, 35 cases) and measurement of hemodynamics revealed the following. In all pacing modes, atrial contraction was observed in cases of advanced atrioventricular block. However, in the VVI pacing mode with sick sinus syndrome, atrial contraction was often lost. In sick sinus syndrome group Ⅲ, pacemaker non-mediated arrhythmias were often recorded. Pacing failure was not noted with any atrial or ventricular pacing. Undersensing was observed in 26% of the AAI pacing group and 7% of the VVI pacing group. Myopotential inhibition was observed in 11-24% of all pacing modes, but only two patients complained of subjective symptoms. DDD pacing with atrial sensing yielded effective increase of heart rate, but caused pacemaker tachycardia and pacemaker mediated tachycardia. In making these diagnosis and managing of pacemaker mediated arrhythmias, 24-hour Hotter recordings were the most effective. In comparison of hemodynamics in any pacing mode, physiological pacing was significantly different from VVI pacing as to blood pressure, left atrial pressure and cardiac index. Patients who require improvement of hemodynamics should be treated with physiological pacing. As for the optimal choice of pacing modes, patients with advanced atrioventricular block without underlying disease do not always require physiological pacing. However, the patients with sick sinus syndrome should receive physiological pacing.