adjoining the catheterized femoral artery or in the external jugular vein for the injection of the test materials a catheter in the left ventricle through a common carotid to record the ventricular pressure and its first derivative dp dt a catheter in the coronary sinuses two dogs for the withdrawal of venous blood in the left coronaries a thin hypodermic needle 246 connected to a catheter in the left circumflexed coronary artery for the intracoronary injection of the test substances the oxygen content in the coronary sinuses was measured with a van slyke apparatus the studies have been performed on the dogs 4 6 days after the installation of an electromagnetic flux transducer on the ascending aorta a catheter in the ascending aorta to register the blood pressure and a catheter in the external jugular vein for endovenous injections this surgical preparation was performed under anaesthesia with sodium pentathol 30 mg kg under sterile conditions during the experiment the animals are allowed to remain quiet on a padded bed without sedatives and without restraining means they were used to measure the cardiac output left ventricular work per minute cardiac throw for mean aortic pressure length of the sistule ejection phase and the first derivative of the curve of aortic flux df dt together with the blood pressure and cardiac frequency to measure the blood flow and blood pressure there were used respectively biotronex no 610 amplifiers and battaglia rangoni no 1 1a transductors the data have been visually observed on a hewlett packard 4588.