Briefly, after the induction of anesthesia and the placement of TEE, hemodynamic variables (pulmonary and systemic blood pressure, central and pulmonary venous pressure, cardiac output, calculated SVR, etc.) will be collected. In addition, left ventricular performance (including estimates of LVEDV, LVESV, EF, FAC, etc.) will be assessed using TEE. Once these baseline data are recorded, the ITPR will be inserted in the anesthesia circuit and activated to provide -9 mmHg ETP. After the ITPR has been active for at least two minutes, the same hemodynamic and TEE data obtained above will be gathered. After the data is recorded, the ITPR will be disconnected and no further interventions will be made. In addition to the hemodynamic and echocardiographic data described above, an arterial blood gas will be obtained from the pre-existing radial artery catheter during the on- and off- states.