Backgroud : The synchrony of pacing heart may be affected by RV pacing site and important in pacemaker patients for cardiac function. The mechanism of dyssynchrony includes regional delays of both ventricular contraction and relaxation. Dyssynchrony may be inter- or intraventricular, and echocardiography may evaluate both types through several techniques. We evaluated the cardiac dyssynchrony according to RV sites (RV apex vs mid-septum) in normal systolic functioned patients with narrow QRS. Methods : RV apex and mid-septal pacing was performed in 12 patients (4 men, 8 women; age, 53.2 짹 12.4 years). Transthoracic echocardiography at rest and during pacing were performed in all patients. We measured both interventricular and intraventricular dyssynchrony by echocardiography. Interventricular dyssynchrony was performed by measuring the time between ventricular ejections (the time interval between the beginning of the systolic wave of pulmonary and aortic ejection) and by measuring the time between septal contraction and posterior wall contraction though the M-mode. Intraventricular dyssynchrony was performed by measuring the time between the beginning of the QRS complex and the peak systolic wave of tissue Doppler (between the septal and lateral basal wall). Results : Results are presented in Table 1. Conclusion : The RVA pacing is superior to mid-septal pacing for intraventricular synchrony in normal systolic functioned patients with narrow QRS.