Relation of Ultrastructure to Function in the Intact Heart: Sarcomere Structure Relative to Pressure Volume Curves of Intact Left Ventricles of Dog and Cat

Reproducible pressure-volume curves have been obtained from fresh left ventricles removed from 10 cats and 27 dogs. Electron microscopic observations of sarcomere length and structure in the walls of these chambers have been correlated with the parameters of passive filling. In both the dog and the cat a similar relation of sarcomere length to filling pressure is observed, a filling pressure of 12 mm Hg corresponding to a sarcomere length of 2.2 µ. Sarcomeres shorter than 1.85 µ are not observed under conditions of passive filling. Sarcomeres tend to be longest in the inner layer of the ventricular wall. Filling pressure is observed to be a more general and reproducible index of sarcomere length than absolute or normalized filling volume. H zones are often present in the sarcomeres of the ventricular wall with filling pressures greater than 15 mm Hg and sarcomeres greater than 2.3 µ in length. These findings are discussed in relation to previous studies of papillary muscle and in relation to mathematical models for the left ventricle. The present results indicate that the normal left ventricle functions along the ascending portion of the length-tension curve, where the end diastolic sarcomere lengths are 2.2 µ or less.