By temporary substitution for the left ventricle is meant its complete bypass temporarily by all of the blood that normally passes through it. This is accomplished by withdrawing the blood from the left atrium, passing it through the artificial left heart, and returning it to the aorta by way of the left subclavian artery. The systemic circulation is thereby artificially maintained while the right heart and the lungs continue to perform their functions. EXPERIMENTAL BACKGROUND Several investigators have artificially maintained the systemic circulation in animals using methods in which the blood bypasses the left ventricle. Sirak, Ellison, and Zollinger1 reported on a mechanism with which cardiotomy of the empty left ventricle could be performed. Bypassing of the left ventricle by the blood was used by Kantrowitz and Kantrowitz2 in experimental animals. Wesolowski and Welch3 also reported on such a mechanism. We previously reported on our experimental work