The Contractile Properties of Human Heart Muscle: Studies on Myocardial Mechanics of Surgically Excised Papillary Muscles*

Previous studies of the performance character-istics of the heart have usually been directed to its function as a pump and, therefore, have been concerned principally with measurements of in-travascular and intracardiac pressures, flows, and derivatives of these variables. Over the past three decades, extensive studies of skeletal muscle have provided an understanding of the mechani-cal behavior and energetics of this tissue (1-5). Recent studies of isolated segments of mammalian heart muscle (6-8) have permitted extension of this approach to the myocardium and have sug-gested the feasibility of analyzing the perform-ance of the ventricle in terms of its properties as a muscle (9-12). Although efforts have been made to characterize normal and abnormal func-tion of the human heart from this point of view (13-15), a necessary first step is a detailed de-scription of the mechanical properties of human heart muscle. Such a description-is presented in this report, and a direct extension of these in-vestigations to the intact human ventricle is the subject of the companion paper (16). Methods Left ventricular papillary muscles were obtained at the time of mitral valve replacement in 19 patients. The pa-tients ranged in age from 21 to 64 years; 13 were males and 6 were females. The major hemodynamic abnor-mality in 8 patients was mitral regurgitation, in 5 pa-tients it was mitral stenosis, and in 6 patients combined stenosis and regurgitation were present. Five patients had associated aortic valve disease, and in 4 of the 19 pa-tients the aortic valve was also replaced with a prosthesis * Submitted for publication December 28, 1964; ac-