OBJECTIVES: We sought to determine whether abnormal myocardial blood flow (MBF) responses to the cold pressor test (CPT) in patients with various risk factors may involve different mechanisms that could lead to varying responses of short- and long-term administration of antioxidants. BACKGROUND: There is a growing body of evidence that increased vascular production of reactive oxygen species markedly reduces the bioavailability of endothelium-derived nitric oxide, leading to impaired vasodilator function. It is unknown whether increased oxidative stress is the prevalent mechanism underlying endothelial dysfunction in patients with different coronary risk factors. METHODS: Fifty patients with normal coronary angiograms were studied. The MBF responses to CPT was determined by means of positron emission tomography before and after intravenous infusion of 3 g vitamin C or saline (placebo), as well as after 3 months and 2 years of 2 g vitamin C or placebo supplementation daily. RESULTS: In hypertensive patients, the change in MBF (AMBF) was not modified significantly by short-term vitamin C administration challenges (0.20 ± 0.20 ml/g/min; p = NS) but was significantly increased after three months and two years of treatment with vitamin C versus baseline (0.58 ± 0.27 and 0.63 ± 0.17 vs. 0.14 ± 0.18 ml/g/min; both p ≤ 0.001). In smokers, ΔMBF in response to CPT was significantly increased after short-term vitamin C infusion and long-term vitamin C treatment (0.52 ± 0.10, 0.54 ± 0.13, 0.50 ± 0.07 vs. -0.08 ± 0.10 ml/g/min; all p ≤ 0.001). In hypercholesterolemic patients, no improvement in ΔMBF during CPT was observed after short- and long-term vitamin C treatment (0.05 ± 0.14, 0.08 ± 0.18, 0.02 ± 0.19 vs. 0.08 ± 0.16 ml/g/min; p = NS). The CPT-induced ΔMBF in hypertensive patients and smokers after follow-up was significant as compared with placebo and control subjects (p ≤ 0.001). CONCLUSIONS: The present study revealed marked heterogeneous responses in MBF changes to short- and long-term vitamin C treatment in patients with various risk factors, which highlights the quite complex nature underlying abnormal coronary vasomotion.