Pressure-circumference relations of left ventricle.

Changes in left ventricular pressure and left ventricular circumference of intact animals have been recorded simultaneously during spontaneous and induced cardiovascular responses. Mechanisms by which the left ventricular myocardium alters its ‘work output’ are indicated by pressure-circumference loops displayed on a cathode ray oscilloscope. Evidence is presented that the external work of the heart is not necessarily related to the diastolic dimensions in accordance with Starling's law of the heart. Instead, changes in both myocardial contractility and distensibility may play important roles in cardiac adaptation to various conditions.