Development of bilateral ventricular hypertrophy in animals exposed to sustained hypoxia is demonstrated. Female Sprague-Dawley rats (180-200 g) were subjected to acute (0.40 atm/24 h) or chronic intermittent (0.40 atm/18 h/day/7days) hypobaric hypoxia. Control animals were maintained at room pressure. The changes in ventricular mass (right ventricle and left ventricle including the septum) were evaluated on the basis of the dry weight values immediately at the end of hypoxic stimulus. Data show that both acute and chronic hypobaric hypoxia allow rate to develop a significantly degree of hypertrophy in the left as well as in the right ventricle. The factors involved in the genesis of the left ventricular hypertrophy in hypoxic conditions are presented.