OBJECTIVE. The objective of our study was to compare the image quality of cardiac CT images of mechanical valves in patients with irregular heart rates (HRs) using absolute-delay multiphase reconstruction versus relative-delay multiphase reconstruction. MATERIALS AND METHODS. A total of 26 patients with 40 mechanical valves who had atrial fibrillation during CT were included. The image quality of the CT scans was assessed for the subvalvular and valvular regions on a 4-point scale. The paired t test or Wilcoxon signed rank test was used to compare image quality scores between the relative-delay and absolute-delay reconstruction techniques. The overall image quality score was determined as the mean of the valvular and subvalvular region scores. RESULTS. For valvular regions, the image quality scores were 2.93 +/- 0.73 (mean +/- SD) for the relative-delay reconstruction technique and 3.55 +/- 0.60 for the absolute-delay reconstruction technique (p < 0.0001). For subvalvular regions, the image quality scores were 2.8 +/- 2.80 +/- 0.79 and 3.35 +/- 0.66 for the relative- and absolute-delay reconstructions (p < 0.0001), respectively. The nondiagnostic image quality group consisted of relative-delay reconstruction images of three valves (7.5%); the image quality scores for the absolute-delay reconstruction images of all three valves were improved, and the absolute-delay reconstruction images of the three valves were of diagnostic quality (p < 0.0001). CONCLUSION. Absolute-delay multiphase reconstruction can improve CT image quality of mechanical valves in patients with an irregular HR compared with relative-delay reconstruction.