Objective-This study was to investigate the effects of chronic exercise on vasodilatation and endothelial intracellular calcium (EC [Ca 2ϩ ] i ) signaling in atherosclerotic animals. Methods and Results-For 8 weeks, male New Zealand White rabbits were fed rabbit chow with or without the addition of 2% cholesterol. They were further divided into control and exercise groups. Animals in the exercise groups ran on a leveled treadmill at 0.88 km/h for 10 to 60 minutes gradually for 5 days per week for a total of 8 weeks. At the end of experiments, femoral arteries were dissected, loaded with fura 2-AM, and mounted in a tissue flow chamber. PE-precontracted vessel specimens were exposed to acetylcholine (ACh). The EC [Ca 2ϩ ] i elevation and vasorelaxation were determined simultaneously under an epifluorescence microscope equipped with a ratio-imaging capability. Our results showed the following: (1) high cholesterol diet feeding caused lipid deposition on vascular surface, reduced the ACh-evoked EC [Ca 2ϩ ] i elevation, and impaired endothelium-dependent and endothelium-independent vascular responses, but chronic exercise had the opposite effects; (2) ACh-induced vasorelaxation was associated with EC [Ca 2ϩ ] i elevation in all groups; and (3) vasorelaxation at high levels of EC [Ca 2ϩ ] i elevation decreased in hypercholesterolemia. Conclusions-Our data suggest that hypercholesterolemia induces vascular structural changes and impairs EC [Ca 2ϩ ] i signaling and vasodilatation, whereas chronic exercise partially reverses these adverse effects. Key Words: chronic exercise Ⅲ high cholesterol diet Ⅲ nitric oxide Ⅲ calcium signaling Ⅲ vasodilators A therosclerosis is the leading cause of mortality in the developed world, and it is possibly caused by a high-fat diet and a sedentary lifestyle. 1 Risk factors of atherosclerosis, ie, elevated LDL cholesterol levels, diabetes mellitus, hypertension, homocystinemia, and smoking, are associated with vascular dysfunction, such as monocyte adhesion and invasion, smooth muscle proliferation and migration, platelet activation, and extracellular matrix formation. 2 Moreover, the atherogenesis-related endothelial impairment occurs well before any detectable structural changes of the vessel wall. 3 Normally, the vascular endothelial cells release NO. 4 NO relaxes vascular smooth muscle, inhibits platelet adhesion/ aggregation, inhibits monocyte adhesion and migration, reduces the production of superoxide, inhibits oxidation of LDL, and inhibits smooth muscle proliferation and migration. Therefore, it is considered to be an endogenous antiatherosclerotic factor. 5 It is likely that the impairment of endothelium-derived NO activity is a cause, not a consequence, of atherosclerosis.Current consensus indicates that regular exercise reduces the incidence of cardiovascular diseases and death or causes a regression of symptoms. 1,6 -8 Several possible mechanisms of these exercise effects have been proposed, such as an increase in HDL cholesterol level, 9,10 a decrease in the oxi...