['To compare the agreement of cardiac index measurements between transesophageal echocardiography across the prosthetic mitral valve and the continuous thermodilution method through a pulmonary artery catheter (PAC-TD) in patients undergoing double-valve replacement.', 'Observational prospective study.', 'University hospital.', 'Twenty-five patients undergoing double-valve replacement (12 men and 13 women, age 25-78 years, ASA III-IV, NYHA II-III, LVEF≥45%). Patients were grouped according to their prosthesis (mechanical prosthesis v bioprosthesis).', 'All patients underwent cardiac index assessment during double-valve replacement.', 'Cardiac index across the prosthetic mitral valve was measured simultaneously using transesophageal echocardiography (CI(MV)) and PAC-TD (CI(PAC)) at 15, 30, 45, and 60 minutes after weaning from cardiopulmonary bypass, and at 0, 15, and 30 minutes after incision closure. A correlation was present between CI(MV) and CI(PAC) in both groups (mechanical prosthesis: r = 0.47, p<0.01; bioprosthesis: r = 0.60, p<0.01). In the mechanical prosthesis group, the bias between techniques (CI(PAC) v CI(MV)) was-0.5 L/min/m(2) (95% CI:-1.97 to 0.97), and error was 55%. In the bioprosthesis group, the bias between both techniques was-1.3 L/min/m(2) (95% CI:-3.1 to 0.5), and error was 56%.'] Is transesophageal Echocardiographic Measurement of Cardiac Index by the Prosthetic Mitral Valve Method Similar to the Continuous Thermodilution Method Via a Pulmonary Artery Catheter?