A stimulated altitude of 7000 m was applied in rats chronically exposed to hypoxia in a hypobaric chamber. In these experimental conditions the contralateral ventricle not exposed to pressure overload (that is, the left) showed a significant degree of hypertrophy. The hypoxic stimulus did not affect systemic artery pressure or the heart rate. Chronic adrenergic stimulation performed in the rat treated with low doses of isoprenaline (a direct stimulating adrenergic drug) or with tyramine (primarily a releaser of endogenous catecholamines) induced hypertrophy of the right ventricle, left ventricle, and interventricular septum without modifying the haemodynamic parameters mentioned above. The development of ventricular hypertrophy in the absence of pressure overload is stressed. A role for neurohumoral factors (that is, adrenergic stimulation and catecholamines) in the development of ventricular hypertrophy is suggested.