PURPOSE: We wanted to investigate the influence of heart rate (HR) and its variations on the CT angiography (CTA) image quality with using 16- and 64-slice multidetector CT (MDCT). MATERIALS AND METHODS: Of the 200 recruited patients, 100 underwent 16-slice MDCT (M:F=74:26, median age: 55.2 +/- 12.8 years) and 100 underwent 64-slice MDCT (M:F=68:32, median age: 58.4 +/- 11.6 years). We evaluated the image quality with respect to the HR and the variations in the HR. The images were graded in terms of the quality of vessel depiction with using a four-point scoring system from 1 to 4, where 4 represented the best image quality. In addition, we analyzed the 16- and 64-slice MDCT images in terms of the presence and frequency of stair-step artifacts. RESULTS: The mean HR variation was significantly lower on 64-slice MDCT than that on 16-slice MDCT (5.48 +/- 4.20 bpm vs. 10.31 +/- 5.90 bpm, respectively, p < 0.05). The mean image quality score of 64-slice MDCT was significantly greater than that of 16-slice MDCT (3.40 +/- 0.36 vs. 2.75 +/- 0.43, respectively, p < 0.05). The frequency of stair-step artifacts was markedly greater for 16-slice MDCT (2.4 +/- 3.2 vs. 0.5 +/- 1.04, respectively, p < 0.05). CONCLUSION: 64-slice MDCT provides better image quality because it reduces the scan times and minimizes the HR variations.