Use of protease inhibitors (PI) in HIV patients is associated with hyperlipidemia and increased risk of CHD. Chronic systemic and cardiac effects of ritonavir (RTV), a universal PI booster, and Mg-supplementation were examined. RTV was administered (75 mg/kg/day p.o.) to LewisXBrown-Norway hybrid (LBNF1) rats for up to 8 weeks; significant increases in plasma triglyceride and cholesterol occurred from 8 days to 8 weeks. At 5 weeks, the expression of selected hepatic genes (CYP7A1, CITED2, G6PC, and ME-1), which are key to lipid catabolism/synthesis, were altered towards lipogenesis. Dietary Mg-supplementation (6-fold higher) completely reversed the altered expression of these genes, and attenuated both hypertriglyceridemia and hypercholesterolemia. Neutrophils isolated from the RTV treated rats displayed a 3-fold higher basal and a 2-fold higher stimulated superoxide production; plasma isoprostane and RBC GSSG levels were elevated 2-3-fold. All oxidative indices were normalized by Mg-supplementation. After 5 weeks, RTV caused significant decreases in cardiac left ventricular (LV) shortening fraction and LV ejection fraction; mitral valve E/A ratio was reduced accompanied by LV posterior wall thinning. Immunohistochemical staining revealed significant WBC infiltration (5-wks) and prominent fibrosis (8-wks) in the RTV hearts. Mg-supplementation attenuated RTV-induced declines in systolic and diastolic function (>70%), improved mitral E/A ratio and lessened LV posterior wall thinning (by 75%), and substantially decreased the pathological markers. Conclusions: The known clinical hyperlipidemia effects of RTV could be mimicked in the LBNF1 rats; in association, systemic oxidative stress and progressive cardiac dysfunction occurred. Remarkably, Mg-supplementation alone suppressed RTV-mediated hyperlipidemia, oxidative stress and cardiac dysfunction.