A commentary on muscle mechanics.

• Numerous studies of cardiac muscle mechanics have produced contradictory conclusions. The present paper discusses a few salient points about cardiac muscle mechanics, but it is not a critical review of the literature such as that recently published by Jewell and Blinks (1). An analysis of ventricular contraction is also presented; we hope that it will stimulate fresh thought about the relationship between isolated muscle experiments and the functioning of the intact heart. Isolated muscle experiments on papillary muscles have, in many cases, been made in an overly optimistic manner. The literature of only a few years ago suggests that cardiac muscle mechanics is a highly quantitative science operating on universally accepted, well-defined principles. More recently, however, the tenuous state of our knowledge has been recognized by many investigators: classical theories are being attacked and entirely new viewpoints are being advanced. This situation makes the study of cardiac muscle mechanics academically challenging but causes no little consternation for cardiologists and others who desire practical parameters of cardiac performance based on fundamental physiology. The application of the concepts of skeletal muscle mechanics to isolated cardiac papillary muscle demonstrated by Abbott and Mommaerts (2) stimulated a large body of work which tended to emphasize the common principles of the two fields (1). In these efforts, however, the important differences between cardiac and skeletal muscle were not always appreciated (3, 4). These studies were made assuming an analogy between cardiac muscle contractions and contractions of frog skeletal muscle with its parallel fibers that run the length of the muscle. This analogy is poor because the