Abstract: Objective: To evaluate the value of narrow acquisition acquisition CTCA by single cardiac cycle using 320-detector row CT. Methods: 80 patients(HR ≤ 65 bpm, HRv ≤ 5 bpm) were enrolled from september 2015 to January 2016 in this study. All of patients were divided into two groups. Group A included 40 patients with acquisition phase 70%~80% in R-R interval and Group B with acquisition phase 30%~80% in R-R interval. Both two groups with tube voltage 100 k V and tube current tailored to BMI(300~580 mA). Two groups were evaluated by radiation dose and image quality(all coronary artery segments scaleand percentage of assessable, aorta attenuation). A P value below 0.05 was considered to be statistically significant. Results: All patients include group A and B successfully underwent single cardiac cycle CTCA. The mean effective dose for group A was 2.02 mSv ± 0.78 mSv; this represents a 46% reduction as compared with that group B(4.35 mSv ± 0.85 mSv,t=-12.474,P=0.000). The mean image quality score was 3.61 ± 0.53 obtained with Group A versus 3.71 ± 0.48 obtained with Group B(Z=-3.074,P=0.002). The difference of the percentage of assessable coronary artery segments in both groups was not statistically significant(χ²=0.215,P=0.643). The difference of aorta attenuation in both groups was not statistically significant(t=-1.132,P=0.261). Conclusions: narrow acquisition acquisition CTCA may reduce the radiation dose keeping image quality assessable in patients with low HR(≤ 65 bpm) and HRv(≤ 5 bpm).