The purpose of this study is to determine sevoflurane's dose-dependent effect on left ventricular (LV) function in cardiac surgery. The change of tissue Doppler imaging (TDI) of lateral mitral valve annular velocity at three different sevoflurane concentrations would be analyzed by using intraoperative transesophageal echocardiography (TEE)in cardiac surgery patients.

Following data would be determined after 10 min-exposure to each dosage of sevoflurane with 1.0, 2.0 and 3.0 inspired vol% (T1, T2 and T3, respectively) during remifentanil-based anesthesia (1.0 mcg/kg/min) for cardiac surgery (n=14):

1. TDI of lateral mitral annulus at systole (S'), early filling (E') and atrial contraction (A')
2. transmitral flow Doppler at early filling (E), atrial contraction (A), deceleration time;
3. LV-ejection fraction (EF)
4. bispectral index (BIS)
5. phenylephrine-infusion rate
6. other pressure derived hemodynamic parameters:heart rate; systolic, diastolic, and mean blood pressures; systolic, diastolic, and mean pulmonary artery pressures; central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), mixed venous O2 saturation (SvO2), cardiac index (CI) and stroke volume index (SVI)

Inclusion Criteria:

• patients undergoing cardiac surgery

Exclusion Criteria:

• low ejection fraction < 50% in preoperative transthoracic echocardiography
• atrial fibrillation
• pacemaker
• pericardial and infiltrative myocardial disease
• mitral annular calcification, surgical rings, prosthetic mitral valves
• lateral left ventricular regional wall motion abnormality
• esophageal spasm,stricture, laceration, perforation, and diverticulum
• diaphragmatic hernia,
• history of extensive radiation to the mediastinum
• upper gastrointestinal bleeding