The concept of "end-systolic" pressure-volume and length-tension relations of the heart from a muscle physiologist's point of view.

End-systolic length-tension relationships were measured on ultrathin isolated heart preparations of rat (mean diameter +/- S.D. = 96 microns +/- 45 microns). Independent of contractile state being changed by variation in extracellular Ca++-concentration no unique end-systolic length-tension relation was found when varying pre- and afterload over a wide range. It is more likely that rectilinear end-systolic curves can be obtained under a low contractile state than under a high one. Thus, the muscle physiological basis is withdrawn from the Emax-concept for which a single end-systolic pressure-volume relation is typical.