The aim of this study was to test the hypothesis that subchronic co-application of vitamins B6 and folic acid (FA) could affect heart failure (HF) induced by monocrotaline (MCT), with the modulation of oxidative stress parameters and cardiometabolic biomarkers. Biochemical and histomorphometric analyses were assessed in blank solution-exposed controls (C1 physiological saline 1 mL/kg, 1 day, n = 8; C2 physiological saline 1 mL/kg, 28 days, n = 8), MCT-induced HF (MCT 50 mg/kg, n = 8), B6+FA (vitamin B6 7 mg·kg^–1·day^–1, FA 5 mg·kg^–1·day^–1; n = 8), and MCT+B6+FA (MCT 50 mg/kg, vitamin B6 7 mg·kg^–1·day^–1, FA 5 mg·kg^–1·day^–1; n = 8) in male Wistar albino rats (body mass 160 g at the start). Superoxide dismutase and glutathione peroxidase activities, thiol-, carbonyl groups, and nitrotyrosine were determined in cardiac tissue. Echocardiography was performed to confirm MCT-induced HF. The right ventricular wall hypertrophy, accompanied with significant increase of troponin T and preserved renal and liver function, has been shown in MCT-induced HF. However, these effects were not related to antioxidant effects of vitamin B6 and FA, since several parameters of oxidative stress were more pronounced after treatment. In this study, co-application of vitamins B6 and FA did not attenuate hypertrophy of the right ventricle wall but aggravated oxidative stress, which is involved in HF pathogenesis.