Gordon, Michael Solomon

Ouabain had no effect on myofibrillar adenosine triphosphatase (ATPase) activity in normal, hypertrophic, and failing hearts with concentrations of calcium chloride varying from 0 to 5.0 mM. The quantitative effects of CaCl 2 on myofibrillar ATPase were the same in all groups studied. At necropsy it was found that myofibrillar ATPase activity of heart tissue from patients with clinical and pathologic diagnoses of failure from left ventricular volume and pressure overload was significantly lower than that of normal controls. The ATPase activity in patients with failure due to right ventricular volume and pressure overload was not significantly lower than that in normal controls. There was no difference in myofibrillar ATPase activity between normal left and normal right and between failing left and failing right ventricles. The difference demonstrated at necropsy between normal and failing hearts was not a function of age or of hypertrophy per se. Myofibrillar ATPase activity of hypertrophic nonfailing surgical pulmonary infundibular tissue was the same as that of normal postmortem ventricles. The ATPase activity of failing surgical papillary muscle in a small number of experiments was in the range of that found in failing postmortem ventricles.