The deficiency of methionine, an essential amino acid, is associated with cardiovascular lesions. Because different types of cardiac pathologies are caused by a decrease in antioxidants, we examined the effects of methionine on myocardial antioxidant enzymes in hemodynamically assessed rats that were treated with methionine (10 mg/ml) in drinking water for 12, 24, and 48 h. Glutathione peroxidase (GSHPx) activity was significantly increased to 150.5 ± 12.2 and 191.7 ± 13.7% of the control value at 12 and 24 h, respectively, followed by a decline to 120 ± 24.6% at 48 h. The mRNA levels of GSHPx at these time points were 151.2 ± 12.0, 218.7 ± 35.3, and 173.5 ± 25.2%, respectively. Superoxide dismutase (SOD) activity was 144.3 ± 3.7, 114.3 ± 10.1, and 143.1 ± 11.2% at 12, 24, and 48 h, respectively. Catalase (Cat) activity was 272.4 ± 5.4, 237.8 ± 16.6, and 224.1 ± 17.3% of the control value. The expression of Cat and SOD mRNA was unchanged at 12, 24, and 48 h. The lipid peroxidation was decreased by 24.4 ± 11.2, 54.9 ± 0.1, and 6.4 ± 2.1% at 12, 24, and 48 h, respectively. Methionine had no effect on the ventricular or aortic pressures, heart rate, and myocardial glutathione levels at any of the time points. The study shows that methionine has a significant effect on the myocardial antioxidant enzyme activities, and only changes in GSHPx enzyme activity correlated with the mRNA changes. These antioxidant changes may have a role in the beneficial effects of methionine in pathological rather than physiological conditions.