We believe that the patient exposure dose differs by heart rate for a coronary computed tomography angiography (CCTA), and we attempted to reduce patient exposure dose of the CCTA. Specifically, we made a clear difference of exposure dose between heart rate and optimal cardiac phase or some imaging methods. Next, we established criterion of the CCTA in our hospital, and usefulness was discussed. For examination methods, patients with a heart rate below 60 beats per minute (bpm) received a high-pitch spiral scan (Flash Spiral mode), those between 61 to 70 bpm received a step and shoot scan (SAS mode), and those of >70 bpm or an irregular heart rate received low-pitch spiral scan (Helical mode). The results of the clinical study showed that patient exposure dose reduced 87% in Flash Spiral mode (1.93±0.26 mSv) and 66% in SAS mode (4.88±1.24 mSv) compared with Helical mode (14.35±3.42 mSv). In our present study, we proved the usefulness of our criteria using CCTA. If the results of our present study become guidelines of CCTA users, we suggest that total patient exposure dose can be reduced.