Asynchronous ventricular activation, induced by left bundle branch block, is known to have deleterious effects on the systolic and diastolic functions of the left ventricle (LV). Cardiac resynchronization therapy (CRT) has been proposed as a complementary method to improve the LV systolic performance by restoring the synchronized contraction patterns in patients with advanced heart failure and left bundle branch block. However, the effect of CRT on myocardial blood flow is not well established. In the present study, we therefore examined the coronary blood flow in 20 patients with idiopathic dilated cardiomyopathy, implanted with a biventricular pacemaker according to the established CRT criteria. Color Doppler settings were adjusted for the optimal coronary flow imaging, and coronary flow velocities were obtained in all patients. Typical diastolic predominant phasic Doppler spectrum of the distal left anterior descending coronary artery (LAD) was recorded. Conventional echocardiographic variables, peak values of the diastolic and systolic LAD velocities, and the velocity time integrals were measured for three or five consecutive beats during CRT with pacemaker on and off. Successful CRT with biventricular pacing increased coronary blood flow velocities of the distal LAD in addition to its well-known benefits on the systolic and diastolic LV performance in patients with significant dyssynchrony. CRT decreased duration of mitral regurgitation and increased diastolic filling time. Peak diastolic velocities and velocity time integral of the distal LAD were increased significantly. In conclusion, successful CRT with biventricular pacing improves coronary blood flow velocities of the distal LAD.