[Determinants of the rate of myocardial relaxation]

The main mechanical determinant of the rate of the myocardium isometric relaxation was found to be the final-systolic length (LK.C.) in cats and frogs. Adrenaline accelerated the relaxation by shortening the LK.C. and by its "own" effect, the latter being obvious in fixed values of the LK.C. An increase in the stimulation rate shortened the LK.C. as well but decelerated the relaxation in fixed values of the LK.C. The mechanisms of control of the rate of the myocardium relaxation, are discussed.