Cardiac resynchronization therapy (CRT) is a treatment modality for selected patients with refractory heart failure. We intended to examine the usefulness of coronary venous system imagining with conventional coronary angiogram before the CRT implantation procedure. A total of 180 patients were scheduled for CRT and were prospectively randomized 1:2 into 2 groups. Group 1 (n = 60) received standard CRT procedure without the guidance of selective left coronary angiography. In group 2 (n = 120), CRT implantation was accomplished with the guidance of the preprocedural coronary angiography. We compared the 2 groups in terms of the total implantation time, total fluoroscopy time, the amount of contrast medium used, and cumulative radiation exposure. The total implantation and fluoroscopy times, the amount of contrast medium used, and cumulative radiation exposure were significantly less in group 2 compared with group 1 (53 ± 7 vs 66 ± 9 minutes, 11 ± 3 vs 20 ± 5 minutes, 24 ± 8 vs 42 ± 14 mL, 26 192 ± 6658 vs 37 388± 9064 mGy cm2, and 253 ± 49 vs 392 ± 79 mGy, P < .0001, respectively). We concluded that coronary angiography prior to CRT implantation is useful in simplifying the procedure, saving time, reducing radiation exposure, and reducing contrast use.