I. The equations of Otto Frank are shown to predict the behavior of manometers whose effective masses and vol. elasticity coeff. are 100 times greater than those of manometers in common use. Applying these equations there was constructed a manometer of adequate frequency (N = 200) and sensitivity which differs from the conventional optical manometer in the following aspects: (1) The cannula at the end of a flexible lead tube can be inserted through the skin into the cavities of the heart or arteries. (2) Pressure pulses can be recorded from the unoperated and unanesthetized animal (or man). (3) Simultaneous records may be obtained from widely separated parts of the cardiovascular system without parallax. Records taken with this manometer differ from those in literature in ways which may be interpreted as due to the absence of shock and anesthesia and due to the fact that the heart was beating normally in the unopened chest.[long dash]II. By means of this manometer, which can be used repeatedly on the unanesthetized animal, femoral pressure pulses accurately calibrated to systolic and diastolic pressures were recorded optically. The subjects investigated were normal dogs and dogs with experimental chronic aortic regurgitation. Their differential responses to epinephrine, amyl nitrite and acetyl-beta-methylcholine chloride are described. The most striking difference between the normal and operated animal is the absence of the usual depressor effects in the latter.