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

Isoflurane is widely used in cardiac surgery patients due to its beneficial effects, but many studies have shown that isoflurane reduces myocardial contractility in a dose-dependent manner, and compromises left ventricular (LV) function.

Tissue Doppler imaging (TDI) of mitral annular velocity during the cardiac cycle has been introduced as a reliable method for analysis of systolic and diastolic LV long-axis function. Efficacy of systolic and diastolic TDI profiles, including systole (S'), early early relaxation (E')and atrial contraction (A') have been suggested to be useful in predicting the impact of isoflurane on LV systolic and diastolic function.

The investigators hypothesized that isoflurane, even at a clinical dosage, would affects intraoperative LV systolic function in a dose-dependent manner and thus produce significant changes int the TDI profiles of systolic mitral annular velocity (S').

So the investigators planned to study the changes in S' of lateral mitral annulus at the clinical isoflurane dosage during remifentanil based anesthesia for cardiac surgery.

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 mediastinum
• upper gastrointestinal bleeding