The investigators hypothesized that predictability of pulse pressure variation (PPV) on fluid responsiveness would be reduced in patients with coronary disease who have diastolic dysfunction.

Inclusion Criteria:

• Patients older than 20 years
• scheduled for elective coronary artery bypass grafting
• normal diastolic function (E/E' < 8) or diastolic dysfunction (E/E' >15) according to preoperative Echocardiographic evaluation

Exclusion Criteria:

• arrythmia,
• reduced left ventricular function (ejection fraction < 40%)
• valvular heart disease requiring concomitant surgical correction
• pulmonary hypertension (mean pulmonary arterial pressure ≥30 mm Hg)
• peripheral arterial occlusive disease, pulmonary disease (asthma, chronic obstructive pulmonary disease, and lung resection)
• end-stage renal disease