Abstract Objectives The effects of hypercholesterolemia (HC) on the myocardium and the underlying mechanisms are unclear. We tested the hypothesis that diet-induced HC-induced myocardial fibrosis by regulating the transforming growth factor (TGF)-β pathway and apoptosis through increased oxidative stress, and that these would be functionally consequential. Methods Three groups of pigs ( n = 6 each) were studied after 12 weeks of normal or 2% HC diet, or HC + antioxidant supplementation. Cardiac function was evaluated by electron beam computed tomography, while fibrogenic mechanisms and apoptosis were evaluated in myocardial tissue. Results HC-induced myocardial fibrosis was accompanied by increased ratio of interstitial collagen I/III (1.4 ± 0.3 versus 0.5 ± 0.1 in normal, p < 0.05), expression of TGF-β1 and its downstream smad mediators, as well as myocyte apoptosis. These alterations were also associated with a decrease in diastolic filling rate compared to normal (134.0 ± 10.6 ml/s versus 70.3 ± 14.3 ml/s, p < 0.05), but were attenuated in HC animals chronically supplemented with antioxidants. Conclusions Myocardial injury elicited by experimental HC includes redox-sensitive increases in TGF-β1 expression and apoptosis, which are associated with diastolic dysfunction. These observations underscore a role of increased oxidative stress in modulating myocardial tissue remodeling and dysfunction in vivo in HC.