[Distensibility of the heart muscle during adaptation to a physical load].

Strips of the papillary muscle of rat left ventricle were extended by means of increasing loads. The curve of the strip elongation depending on the load value characterized the myocardial distensibility. Seven to eleven weeks from the beginning of regular swimming exercises (for 30 to 60 min) the distensibility curve showed a significant increase of the myocardial distensibility, and the maximal contraction amplitude was reached with a lesser force. An increased distension of the cardiac muscle of the adapted animals can serve as one of the components of dilatation of the "trained" heart and a more rapid mobilization of the contractile function during exercises.