A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was if transit-time flow measurement (TTFM) can improve graft patency and clinical outcome in patients undergoing coronary surgery. Altogether 102 papers were found using the reported search, of which 10 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The papers considered for the analysis focus attention on three major topics: intraoperative graft verification with the aim of improving immediate graft patency; predictive power of early- and mid-term graft patency and clinical outcome. Among TTFM parameters, according to different authors, mean graft flow is set at 10 or 15 ml/min; pulsatility index is set at three or five; insufficiency ratio is set by 3 or 4%. We conclude that TTFM is a reliable method to verify intraoperative graft patency. There is some evidence that checking graft patency intraoperatively may improve mid-term outcomes.