Human cardiac myosin: electron microscopic observations.

• Physicochemical studies on cardiac myosin of rabbits and dogs have shown that the myosin molecule is highly asymmetric, measuring about 1600 to 1800 A-' long and having a molecular weight of approximately SOO^OO." Electron micrographs of canine cardiac myosin have confirmed this general morphology, although the molecule appears to be several hundred angstroms shorter than the physicochemical measurements suggest. Detailed studies of human cardiac myosin, normal or pathologic, have not been made because of the practical problems involved in obtaining relatively large amounts of fresh human myocardium. However, quantities of human myocardium sufficient to yield enough myosin for electron microscopic study are frequently available at open heart surgery. Advantage was taken of this circumstance in the present study.