Objective: To evaluate whether the images obtained during the reconstruction window responding to the isovolumic relaxation period (T-T interval: T) could be better in comparison with the images obtained at R-R interval (R) for the patients with heart rate variations. Methods: 26 patients with heart rate variations (the differences of heart rate variation > 10 bpm/min) during the scan underwent 64-detector-row multidetector computed tomography (MDCT) for imaging coronary arteries were enrolled. The images were retrospectively obtained at the optimal phase at around 30% of the R-R interval. Then it compared with the images reconstructed at the isovolumic relaxation period, which is the last portion of the T-wave at the end of the systole. Image quality was analyzed in performed with aorta, RCA, LAD and LCX in each stair-step artifacts and blurring by 2 radiologists (who were not aware of each other���s interpretation). General performance was also assessed. Results: According to analysis of stair-step artifacts, the quality of images obtained at T-T interval were significantly better in the assessment of aorta (T> R: T=R: T< R = 10:14:2) and RCA (T> R: T=R: T< R = 11:11:4). In analysis of blurring, the quality of images obtained at T-T interval were significantly better in the assessment of aorta (T> R: T=R: T< R = 10:15:1), RCA (T> R: T=R: T< R = 9:13:4) and LCX (T> R: T=R: T< R = 6:17:3). General performance was also better in the images obtained at T-T interval (T> R: T=R: T< R = 12:8:6). Conclusion: For the patients with heart rate variations during the scan, the image quality was better in the images obtained during the reconstruction window responding to the T-T interval.