Normal and hypertrophic growth of the rat heart: changes in cell dimensions and number.

The length and width of enzymatically isolated individual rat cardiac myocytes were concurrently measured during normal and stimulated cardiac growth. In normal rats weighing between 75 and 750 g the length and width increased by 64 and 68% while their ratio remained constant (ca. 5.3). The cell volume, calculated on the basis of a cylindrical model, increased almost 5 times. The rates of increase in the volume of an average myocyte and in left ventricular mass were found to be similar, indicating that normal myocardial growth could be explained by hypertrophy of existing myocytes and no proliferation would be required. In cardiomegaly induced by aortic constriction in the adult rat, an increase in cell volume was observed while no significant changes in the length-to-width ratios could be detected. The cell volumes of the hypertrophic hearts corresponded to those observed in hearts of similar weight obtained from larger normal rats and the stimulated cardiac growth could also be explained solely by hypertrophy of existing cells.