Introduction : The second-generation of dual-source CT (DSCT) systems introduced prospectively ECG-triggered high-pitch spiral acquisition mode for coronary CTA with low effective dose and high image quality (IQ).This scan mode used the mean heart rate (HR) of three heart beats before the data acquisition as the predicted heart rate (PHR).The actual HR (AHR) was defined as the cardiac cycle in which the data acquisition was made.If PHR is not equal to AHR, the IQ will be affected.The purpose of our study, therefore, was to assess the influence of the difference between PHR and AHR on IQ in patients with HRs ≤ 60 bpm and evaluate the influence of heart rate variability (HRV) on image quality.