After induction of anesthesia, patients will have their diastolic function evaluated by means of E/e' and other measures. They will then be administered an intravenous bolus of 500 mL of Lactate Ringer® along with passive leg raising (PLR). Stroke volume and fluid responsiveness will be assessed by the thermodilution method (Swan-Ganz catheter) and the FloTrac® device. Fluid responders will be compared to non-responders to evaluate the relationship between E/e' ratio and fluid responsiveness.