We reviewed the comparative trials of the Flotrac/VigileoTM versus the thermodilution method, published in the last five years. The results about the agreement between the two methods measuring cardiac output are contrasting. We also noticed that almost the whole pertinent literature include studies conducted without a correct statistical design, particularly about the sample size. For this reason we consider that results of the published studies about the agreement between pulse contour analysis for cardiac output measurement and thermodilution method may be not reliable.