We compared the accuracy and precision of a non-invasive cardiac output (NICO) monitor and of thermodilution with those of transesophageal echocardiography (TEE) to measure CO in 50 patients who underwent elective valvoplasty to treat TR (26 mild and 24 moderate-to-severe) and in 25 normal controls (without TR). We used TEE as a reference method to measure CO and to intraoperatively grade TR.