The authors investigated the action of prolonged 2- and 3-week action of ethanol on the main parameters of oxidative processes and on the cytochrome content of mitochondria in the heart muscle in 3-month-old rats. They found a statistically significant reduction of the oxidative phosphorylation coefficient, the rate of energy formation and a transient increase of the cytochrome oxidase activity in mitochondria. Under these experimental conditions an increase of cytochromes (cyt aa3, b, c, c1, bc1, c + c1) in mitochondria of the heart muscle occurred.