OBJECTIVE to compare the success rate, radiation dose, image quality and diagnosis of prospective electrocardiogram(ECG)-gated 320-detector computed tomography coronary angiography (CTCA) versus retrospective ECG-gated CTCA. METHODS patients suspected coronary artery disease were divided into two groups which underwent 320-detector CTCA with prospective ECG-gated and retrospective ECG-gated scanning (n = 240 each, HR < 65 bpm). Curved-planar reconstruction (CPR), maximum intensity projection (MIP) and volume rendering (VR) were performed to demonstrate the coronary arteries. The image quality was defined as excellent, good and poor by motion and stair-step artifacts. Effective radiation exposure dose was estimated from the dose-length product. Effective radiation dose, image quality and diagnosis were evaluated. RESULTS the success rate of examination was 100% in prospective ECG-gated group and retrospective ECG-gated group. The mean effective radiation dose of prospective ECG-gated CTCA [(3.3 ± 1.3) mSv] was significantly lower than that of retrospective ECG-gated CTCA [(13.0 ± 1.6) mSv, P < 0.01]. Segments of diagnostic image quality (95.42%, 3435/3600) and non-diagnostic coronary segments (4.58%, 165/3600) in prospective ECG-gated group were similar as those of retrospective ECG-gated group (95.81%, 3449/3600 and 4.19%, 151/3600, all P > 0.05). Compared with CAG, the sensitivity, specificity, false positive and false negative value in prospective ECG-gated group (93.22%, 99.21%, 91.64%, 99.05%) and retrospective ECG-gated group (94.55%, 98.80%, 95.86%, 98.54%) were not significantly different. CONCLUSIONS though the effective radiation dose is significantly lower, the success rate, image quality and diagnosis of prospective ECG-gated 320-detector CTCA is comparable with that of retrospective ECG-gated 320-detector CTCA on patients with stable heart rates less than 65 bpm.