Principle of normal heart adaptation in size and weight to pressure and volume loads

A hypothesis was proposed for a fundamental principle of adaptation of normal hearts to pressure and volume loads: The end-systolic active stress (P) and shortening fraction (S) of myocardium in the ventricular wall were hypothesized to be preserved near normal levels by the adaptation regardless of heart size and animal species F and S were mathematically related to ventricular wall volume (M) and end-diastolic chamber volume (D) both normalized to stroke volume with afterload pressure (P) as a parameter. The deduced M-P and D-P relationships were compared with corresponding data documented in literature. The actual data from normal hearts including pressure and volume overloaded but compensated hearts of different animal species from rats to horses including human children and adults distributed near the theoretical curves for S=0.1-0.2 and F=60-160 Gm/cm2 despite the 2X10(3) times difference in heart size and weight. However, data from failing and abnormal hearts significantly deviated from those curves. These results seem to support the present hypothesis as a fundamental principle of the adaptation of normal hearts to loads.