*If we wish to be really rigorous in examining the applicability of muscle-fibre models to the performance of the intact ventricle, then we must know the velocity of shortening of the contractile element of the muscle, rather than that of the whole fibre; to do this we must either assume that tension is constant through systole (so that the series elastic element is at constant length) or use information about the series element derived from isolated muscle experiments to adjust the velocity of shortening of the whole fibre; even this approach, which was used in deriving Fig. 11.22, is obviously not wholly satisfactory, because it assumes that quantitative results obtained in a very artificial experimental situation are applicable generally in the normal heart.