Adaptation of the rabbit heart to volume load of the left ventricle is characterized by hypertrophic growth. This process involves an increase in the mass and changes in the composition of the myocardium. In the fifth week after perforation of the aortic valve an increase in phospholipid content and in mitochondria and a decrease in protein content was observed in the myocardium. These changes precondition a transient hyperfunction of the cardiomyocytes, but they presumably lead also to the eventual loss of contractile capacity. When the hypertrophic process occurs under conditions of nonspecific beta-adrenergic blockade, the required increase in left ventricular mass is achieved yet the content of phospholipids, proteins and mitochondria remains unchanged. Long-term blockade of beta-adrenergic receptors may be one of the modes of affecting the expression of cardiac genes in such a way that the hypertrophic myocardium does not develop conditions resulting in heart failure.