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Isovolumic and coronary flow preparations were used to test the action of ouabain on the heart and its coronary vascular bed. The former preparation has a left ventricle contracting isovolumically against a balloon in its cavity. In the coronary flow preparation, the input to the left heart is maintained constant with the right heart contracting hypodynamically. Ouabain in the isovolumic preparation produced an increased coronary flow, an augmentation in the magnitude of the left ventricular contraction and cardiac oxygen consumption, and a diminution of oxygen extraction. Apparently ouabain acts here primarily as a coronary dilator and the other changes appear to be secondary. This suggests that ouabain may exert its beneficial effects by lessening the deficiency in coronary flow. Ouabain in the coronary flow preparation also increases coronary flow but by more complex actions. In this preparation, at varying dosage levels, ouabain effects resemble the diphasic action on oxidative metabolism seen in heart muscle slices.
Göksel et al. (1963) studied this question.