The effect of preliminary administration of antioxidant ionol on the heart energy metabolism and contractile function was estimated in hypoxic hypoxia and subsequent reoxygenation. The protective effect of ionol on the energy metabolism in hypoxia was shown to occur mainly at the level of glycolysis. In reoxygenation, the protective effect of ionol manifested at the level of creatine kinase system to provide a rapid restoration of the CP synthesis rate. This shift correlated with the velocity of restoration of the developed pressure and the velocities of contraction and relaxation. On the whole the data obtained correspond to the notion that creatine kinase system and ATP play an important role in the depression and subsequent restoration on the heart contractile function in acute hypoxia and reoxygenation and ionol provides more effective performance of this system and correspondingly more rapid restoration of the contractile function in reoxygenation.