 The clinically widely used X-ray computed tomography examination has a low-grade radiation effect and recently has attracted much attention concerning the possible adverse effects of radiation on human body ref. 1-5. The radiation is harmful to human tissues and cells mainly because it can interact with water which makes up to 80 of cells to generate reactive oxygen species ROS, especially the formation of hydroxyl radicals. So far as we can reach, there is no report concerning the relation between X-ray computed tomography examination and the blood ROS level. Therefore, we wish to conduct this study to clarify if the cardiac computed tomography angiography cardiac CTA may induce a higher level of ROS in the peripheral blood. 