Length-tension diagram and force-velocity relations of mammalian cardiac muscle under steady-state conditions.

Length-tension diagrams and force-velocity relations of isolated cat papillary muscles were measured under strictly stationary conditions: any analysis of isometric mechanograms was carried out only in stable isometric beats; each measurement in beats under any condition different from the isometric one was determined in the very first contraction after a period of stabilization under isometric conditions. The length-tension diagrams show a clear distinction between isometric and isotonic length-tension curves. Force-velocity curves on the basis of afterloaded isotonic, as well as of damped quick-release contractions, could be satisfactorily approximated by a polynomial of the 5th order. Vmax estimated on the basis of afterloaded and of damped quick-releases in the course of isometric and isotonic contractions, was significantly dependent on preload. This is also valid in a range of muscle length which is regarded as physiological.