Inclusion Criteria:  adult patients, scheduled for elective laparotomy (>3h predicted) and requiring a FC.  Exclusion Criteria:  any recurrent cardiac arrhythmia; reduced left (ejection fraction < 30%) or right (systolic peak velocity of tricuspid annular motion < 0.17 m/s) ventricular systolic function.  Once enrolled, the patient can be additionally excluded due to the occurrence of one of the following intraoperative conditions:  significant bleeding (more than 500 ml in ½ hour) recurrent extrasystoles persistent low quality of the arterial signal affecting hemodynamic monitoring measurements intraoperative hemodynamic instability requiring the persistent use of vasopressors.