Hemodynamic modifications induced by general anesthesia could lead to underestimation of mitral regurgitation (MR) severity in the operating department and potentially serious consequences. The intraoperative severity of MR was prospectively compared with the preoperative baseline evaluation using dynamic quantitative transesophageal echocardiography in 25 patients who were stable with MR 2/4 or greater undergoing coronary bypass, mitral valve operation, or both. Significant changes in the severity of MR using transesophageal echocardiographic criteria occurred after the induction of general anesthesia and with phenylephrine. Quantitative transesophageal echocardiographic evaluation of MR using effective orifice area and vena contracta, and the use of phenylephrine challenge, were useful to avoid underestimating MR severity in the operating department.