Background:Prolonged QRS duration(QRSd) is manifestation of delayed ventricular electrical activation, which may result in mechanical dyssynchrony. Mechanical dyssynchrony may result in impaired hemodynamic performance, increased risk of heart failure and death. Baseline QRS duration more than 120msec was suggested to be associated with increased risk of death during pacemaker therapy for sick sinus syndrome. In Korea, there has been no reported data proving this suggestion. Therefore, we investigated association of prolonged QRS duration with death in a pacemaker therapy for sick sinus syndrome. Methods: Between 1990 and 2004, 253 patients (122 male, mean age; 59짹15 years) with SSS had undergone ventricular (n= 88) or dual chamber (n= 165) pacemaker implantation for SSS. Baseline QRSd from 12-lead ECGs before pacemakerimplantation were analyzed. Clinical outcomes including total death, cardiac death, and heart failure(HF) hospitalization were compared between normal baseline QRSd group (QRSd < 120, n=206, 81.4%) and prolonged baseline QRSd group(QRSd ���120, n=47, 18.6%). Results: In total patients, 17(6.7%) deaths occurred (normal QRSd ;n=11, 5.3%, prolonged QRSd;n=6, 12.7%) during follow up. The one patients in normal QRSd qroup died with sudden cardiac death and the two patients in same group died with heart failure. 5- year survival was 95% in normal QRSd group and 90% in prolonged QRSd goup (p=0.08). HF hospitalization occurred in 34 patients (normal QRSd ;n=28, 13.6%, prolonged QRSd;n=6, 12.8%). 5- year HF hospitalization free survival was 90.4% in normal QRSd group and 87.4% in prolonged QRSd group (p=0.91). Conclusion: There was a tendency of more death and HF hospitaliazation in prolonged baseline QRSd group.