To compare the FloTrac/Vigileo TM cardiac output (CO FT/V ) and the MostCare ® /PRAM cardiac output (CO MC/P ) versus transthoracic echocardiographic cardiac output estimation (reference method; CO ECHO ).Prospective observational study.Single center, Cardio-Thoracic and Vascular Surgery/Intensive Care Unit.Patients undergoing elective vascular surgery.Cardiac output measurement with two pulse contour methods: the FloTrac/Vigileo TM and the MostCare ® /PRAM before (T1) and after (T2) fluid loading versus echocardiography (reference method).One hundred fifty-six CO measurements were performed in 26 patients. The data showed poor agreement between CO ECHO and CO FT/V : r 2 = 0.29 (T1) and 0.27 (T2); bias −0.37 (T1) and −0.40 (T2) L/min; limits of agreement from −3.10 to 2.42 (T1) and from −3.0 to 2.2 (T2) L/min. The percentage error was 51.7% (T1) and 49.3% (T2). Conversely, CO MC/P resulted in agreement with echocardiography: r 2 = 0.76 (T1) and 0.80 (T2); bias −0.01 (T1) and −0.06 (T2) L/min; limits of agreement from −1.13 to 1.11 (T1) and from −0.90 to 0.80 (T2) L/min, with a PE of 22.4% (T1) and of 17.0% (T2).In patients undergoing vascular surgery, the FloTrac/Vigileo TM did not demonstrate that it was a reliable system for CO monitoring when compared with echocardiography-derived CO. However, MostCare ® /PRAM was shown to estimate CO with a good level of agreement with echocardiographic measures.