A typical decrease in the blood serum alpha-tocopherol level and red blood cell hemolytic stability was recorded in rats given vitamin E-deficient diet during 2 months. Malonic dialdehyde (MDA) concentration in the skeletal muscles rose 4.5-fold, and in the myocardium, 1.6-fold as compared to the control. During aerobic incubation of heart homogenates of the experimental animals the MDA accumulation rate increased significantly, while that of the skeletal muscle homogenates was little changed. Vitamin E-deficiency induced no essential impairment of the myocardial contractility, however, the fibrillation electric threshold was decreased. The role of vitamin E-deficiency and lipid peroxidation activation in the growth of heart injury due to the factors inducing arrhythmia and fibrillation has been discussed.