[Potentiation and restitution of the myocardial contractility of rats adapted to physical stress].

Initial contractile amplitude of the myocardial strips determined the inotropic response to paired stimulation. The higher the initial amplitude -- the lesser the degree of potentiation and the greater the degree of contraction restitution. At equal amplitudes the myocardial strips taken from rats adapted to exercise showed a greater degree of potentiation and a lesser degree of restitution as compared to control. These changes appear to be due to the changes in the ionic transport in the myocardial cells.