Abstract: Objective To investigate the value of coronary angiography by 256-slice CT scanner in free rhythm of the heart. Methods One hundred and sixteen patients who underwent coronary artery examination were enrolled, 86 cases with regular heart rhythm were included in regular heart rhythm group, and 30 cases with arrhythmia were in arrhythmia group. All patients were performed coronary CT angiography(CCTA)by 256-slice CT scanner(Revolution CT)combined with snapshot freeze(SSF)technique. The quality of images, the effective dose(ED), average CT value and signal to noise ratio(SNR)were compared. Results There were no significant between-group differences in age, body mass, and heart rate of scanning(P>0.05), and the two assessors had higher consistence(Kappa=0.95). The CT value［(404.73±50.91)Hu in the regular heart rhythm group versus(386.23±60.25)Hu in arrhythmia group］and SNR ［(16.03±3.21)in the regular heart rhythm group versus(14.86±3.29 )in the arrhythmia group］ showed no significant differences between the two groups(P>0.05). The ED was(3.40±0.73)mSv in regular heart rhythm group, which was significantly lower than(4.99±3.32)mSv in the arrhythmia group(P<0.05). Conclusion 256-slice CT scanner could complete coronary artery scanning for patients with free rhythm while preserving good image quality using, but ED is increased in arrhythmia patients.