Before it is possible to interpret the inspiratory and expiratory changes in the shape and amplitude of right ventricular pressures in the unopened chest, it is necessary to know the correct contour of the pressure curve during normal cardiac cycles uninfluenced by respiration. Inasmuch, however, as the recent studies of Straub, Piper and C. Tigerstedt (left ventricle only) by optically recording manometers reopened the old question as to the existence of a plateau or rounded top in the ventricular pressure curve, an attempt was made not only to reinvestigate the contour of the curve but to explain the causes of the different records obtained. The changes of right ventricular pressure were, therefore, studied in open chest experiments (in which a right auricular pressure equal to intrathoracic was maintained) by inserting a sharp cannula of an optical manometer with high vibration rate through the musculature near the base of the right ventricle. The instrument and method were demonstrated. The results show that the curve obtained depends, in a large measure, on the sensitiveness and periodicity of the manometer used. (1) With a manometer, periodic for the pressure change involved, all the details described by C. Tigerstedt for the left ventricular curve appear, viz.: an auricular wave, vibrations due to closure of tricuspids, superimposed waves on ascending level, broad, declining top, semilunar vibrations, rapid fall. (2) When the manometer becomes damped so as to become approximately aperiodic, the smaller vibrations on the ascending and descending limb are entirely lost or only faintly indicated. (3) Although many variations of detail occur every record gives evidence of more than an evenly rounded top. During the period of cardiac ejection, the curve rises slowly and reaches a rounded summit and the wave slowly declines until the movement of cardiac relaxation, after which a sudden and abrupt fall occurs.