The effect of ouabain on the frequency-force relation and on post-stimulation potentiation in isolated atrial and ventricular

The relationship between stimulus rate and the force of contraction of myocardial muscle encompasses such phenomena as post-stimulation and post-extrasystolic potentiation as well as the frequency-force curve (for a review see Mom-maerts et al., 1960). The mechanism of potenti-ation has been investigated with metabolic in-hibitors (Katzung et al., 1957), temperature changes (Kruta, 1938; Katzung and Farah, 1956) and changes in hydrostatic pressure (Twente, 1955). The results of these experiments suggest that two processes determine the contractile force. One is a restitution process which is facili-tated as the duration between contractions in-creases; the other is a potentiating process which is facilitated as the duration between contraction