The mechanics of left ventricular contraction in acute experimental cardiac failure

Summary. The effects of acute cardiac failure induced by pentobarbital or pronethalol on the basic mechanical properties of the intact left ventricle were examined in the dog, and the influence on auxotonic and isovolumic contrac-tions of the increase in end-diastolic volume that usually accompanies cardiac failure was assessed. The right heart bypass preparation was em-ployed, and isovolumic beats were induced by sudden balloon occlusion of the aortic root. The ventricular pressure-volume curve was determined di-rectly, and the mechanical responses of the myocardial fibers and contractile elements were calculated. When end-diastolic pressure was held constant, failure reduced the extent of circumferential fiber shortening, and the tension-velocity relation calcu-lated during isovolumic beats was always shifted, with reductions in both maximal velocity (average decrease 30%) and maximal developed tension (average 23%); in addition, during failure achievement of maximal contrac-tile element velocity and maximal tension was delayed, whereas the tota