Abstract: Objective To evaluate triple rule-out CT angiography with prospective ECG-gated 320-detector CT in patients with acute chest pain. Methods Total 170 patients with heart rate ≤70 bpm undergoing triple rule-out CT angiography were divided into group P(prospective ECG gating)and group R(retrospective ECG gating).The images of the coronary arteries,pulmonary artery and thoracic aorta were reconstructed in all patients.All images were processed for image analyses and compared between the two groups. Results No significant difference was showed in the ratio of acceptable segments between two groups.There was no significant difference in CT values ofpulmonary artery [(383.00±53.64)HU vs.(366.48±60.96)HU],coronary artery [(426.31±79.75)HU vs. (407.49±91.00)HU],thoracic arteries [(416.53±63.44)HU vs. (413.58±58.62)HU],noise [(20.46±5.84) vs. (18.55±4.67)],SNR [(22.06±6.47) vs. (23.13±5.76)],CNR [(15.12±5.43) vs.(15.92±4.77)],respectively.However,the significance was found in ED(t=-9.41,P＜0.01). Conclusion Low dose and diagnostic image quality can be achieved with prospective ECG-gated triple rule-out CT angiography.