Minimal invasive monitoring systems of central hemodynamics are gaining increasing popularity. The present study investigates the precision of the esophageal doppler (CardioQ) derived cardiac output and its agreement with pulmonary artery catheter thermodilution (PAC TD) for measuring CO during steady state and with induced hemodynamic changes in patients scheduled for elective cardiac surgery.

Twenty-five patients are planned to be enrolled. After induction of anesthesia, insertion of the PAC and the esophageal-doppler probe, the patient are placed in the following successive positions: a) supine, b) head-down tilt, c) head-up tilt, d) supine, e) supine with phenylephrine administration f) pace heart rate 80 bpm, g) pace heart rate 110 bpm, and CO are measured simultaneously using the CardioQ and PAC TD.

Inclusion Criteria:

• patients scheduled for elective coronary artery bypass grafting (CABG), who are in stable sinus rhythm, who have a left ventricular ejection fraction > 0.40 measured by transthoracic echocardiography, and who have no significant valve pathology

Exclusion Criteria:

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