Direct evidence that left ventricular myocardium is incompressible throughout systole and diastole.

Incompressibility of left ventricular myocardium was tested utilizing isolated canine working left ventricular preparations. This ventricle functioned at levels comparable to the intact heart. The ventricular muscle volume was calculated with the videometric border recognition technique, which is probably the most satisfactory among the presently available techniques to measure left ventricular volume. The calculated wall mass throughout the cardiac cycle varied ranging between about +/- 5%. The difference between the calculated and weighed myocardial mass was within +/- 7% of the true weight. These findings warrant the idea that myocardial muscle mass is incompressible throughout systole and diastole; the assumption used to calculate some variables of left ventricular function.