Editorial: Myocardial sarcomeres and the functioning mammalian heart.

Previously the length-tension properties of the isolated papillary muscle have been related to myocardial sarcomere lengths. Though past studies have relied upon fixed material, recentlly, living muscles have been used. Sarcomere lengths have now been measured on the same specimens in both living and fixed material and the sarcomere length at optimum muscle length established. These lengths are extremely uniform. Studies on the sarcomere lengths through the wall of the left ventricle have also been carried out. Surprisingly sarcomere lengths were relatively uniform from endocardium to epicardium over a wide range of intraventricular pressures. Furthermore, enddiastolic sacarcomere lengths were 91% to 94% of optimum sarcomere length over a physiologic pressure range. Since the papillary muscle in function has been shown to shorten by 23% (to 70% of optimum sarcomere length), these results suggest that the papillary muscle uses the entire ascending limb of the length-tension curve during function.