PURPOSE: To evaluate the mean optimal trigger delays and the difference between the absolute delay and the relative delay as a function of heart rate, using multiphase reconstruction. MATERIALS AND METHODS: A total of 30 patients consecutively underwent a 64-slice MDCT examination. Optimal trigger delays at four planes (the bifurcation of the left main coronary artery, aortic valve, mitral valve and cardiac apex) were measured using multiphase reconstruction based on the absolute and relative delay. For this reason, patients were divided into three groups according to heart rate (group I, < 65 bpm; group II, 65-74 bpm; group III, >= 75 bpm), and the mean optimal trigger delays and the difference between the absolute delay and the relative delay were evaluated at the four planes for each group. RESULTS: The mean optimal trigger delay for the relative delay and absolute delay ranged from 46% to 66% and from 327 to 700 msec, respectively. The differences in the mean optimal trigger delay using the relative and the absolute delay at the four planes were 1% and 4 msec (group I), 3% and 27 msec (group II), and 14% and 46 msec (group III). In group III, the difference of the mean optimal trigger delay based on the relative delay, increased significantly compared to the absolute delay (p = 0.040). CONCLUSION: For the patients analyzed, the results suggest that as the heart rate increased, the mean optimal trigger delays shifted from the mid-diastolic phase to the end-systolic phase and the differences in the mean optimal trigger delay at the four planes were significantly greater for the relative delay.