Objective To investigate the image quality and radiation dose of low heart rate for coronary CT angiography obtained with a prospectively-gated technique volume scan versus a prospectively-gated technique helical scan. Methods Coronary CT angiography obtained with 320-row CT were evaluated in 128 patients. These patients were assigned into two groups: Group 1(n=72), patients undergoing prospectively gated technique volume scan; Group 2(n=56), patients undergoing helical scan. The main branches of coronary arteries were divided into 9 segments. Meanwhile, the image quality was evaluated with a four-point grading scale. The student t test was performed to evaluate the difference between the two groups, which include image noise, excellent rate and pass rate of image, and effective radiation dose. Results The ascending aorta root CT value of group 1 and group 2 were respectively (492.08 ± 58.51) HU and (522.72 ±56.91) HU, and the image noise of the two groups were respectively (19.64 ± 3.51)HU and (22.66 ± 5.33)HU. Coronary artery image quality of group 1 and group 2 both satisfy the diagnosis. Excellent rate were respectively 97.5% (632/648), and 96.8% (488/504), and pass rate were respectively 99.7% (646/648), and 99.2% (500/504), There was no significant difference (p > 0.05)in image noise, excellent rate of image, and pass rate of image between group1 and group2. Effective radiation dose of group 1 and group 2 were respectively (3.21 ± 0.23) mSv, and (13.27 ± 2.39) mSv, The difference in effective radiation dose between the two groups was significant (p = 0.000).Conclusion Image quality of coronary CT angiography obtained with a prospectively-gated technique volume scan and a prospectively-gated technique helical scan can meet clinical diagnosis. As compared with helical scan, radiation dose was much lower when the patient underwent the volume scan. Conclusively, it is a kind of good method of assessment of coronary artery.