Abstract： Objective To evaluate the impact of patient's heart rate(HR)on coronary CT angiography(CTA)image quality(IQ)and reconstruction timing in dual-source CT(DSCT).Methods Ninety-five patients with suspicion of coronary artery disease were examined with a DSCT scanner(Somatom Definition.Siemens)using 32×0.6 mm collimation.All patients were divided three groups according to the heart rate(HR):group 1,HR≤70 beats per minute(bpm),n=26;group 2,HR＞70 bpm to≤90 bpm, n=37;group 3,HR＞90 bpm,n=32. No beta-blockers were taken before CT scan.50-60 ml of nonionic contrast agent were injected with a rate of 5 ml/s. Images were reconstructed from 10%to 100% of the R-R interval using single-segment reconstruction. Two readers independently assessed IQ of all coronary segments using a 3-point scale from excellent(1)to non-assessable(3)for coronary segments and the relationshiD between IQ and the HR. Resuits Overall mean IQ score was 1.31 ±0.55 for all patients with 1.08±0.27 for group 1,1.32±0.58 for group 2 and 1.47±0.61 for group 3. The IQ was better in the LAD than the RCA and LCX(P＜0.01).Only 1.4%(19/1386)of coronary artery segments were considered non-assessable due to the motion artifacts.Optimal image quality of all coronary segments in 74 patients(77.9%)can be achieved with one reconstruction data set.The best IQ was predominately in diastote(88.5%)in group 1,while the best IQ was in systole(84.4%)in group 3. Conclusions DSCT can achieve the optimal IQ with a wide range of HR using single-segment reconstruction. With the increasing of HR,the timing of data reconstruction for the best IQ shifts from mid-diastole to systole.