Background. Right ventricular pacing has deleterious effect on ventricular function due to dyssynchrony caused by RV only pacing(RVO), especially in the patient with heart failure and conduction abnormality. On the contrary, biventricular pacing(BVP) has beneficial effect on cardiac performance and long term prognosis through Resychronization of the dispersed ventricular activation. However the effect of CRT on coronary artery flow is not well established. The aim of this study was to compare the effects on coronary artery flow between BVP and RVO Methods: 7 patients [M:F 5:2, Mean Ejection fraction 31%(20~47%) mean QRS duration 134(120~155ms)] who underwent CRT, were included. Using 12MHz probe, we measured Left anterior descending artery flow transthoracically. Peak diastolic flow velocity(PDF), percent diastolic flow duration(%DD), velocity timie integral of diastolic flow(CVTI) were measured for three consecutive beats during various degree of dyssynchrony by changing interval of sequential LV-RV pacing, and RV only pacing. Degree of dyssynchrony was measured as Septal lateral delay(SLD) of peak systolic velocity of basal myocardial segment, Result: 1.Correlation between SLD and coronary flow were not significant. PDF (r=-0.23, p=0.19), CVTI(r=-0.271, p=0.119), %DD (r=-0.175 p=0.329). 2. The coronary flow was significantly higher in LV-RV sequential pacing with 60ms interval(LV60) compared with RV only pacing(RVO). (table) Conclusion: This results shows that LV-RV sequential pacing in CRT could provide the larger amount of coronary artery flow to myocardium, compared to RV only pacing. Further study should be needed to evaluate the relation between coronary flow and LV dyssynchrony.