Functional assessment of coronary lesions has become an integral part of routine practice in most cath labs. Such evaluation is performed using a pressure wire that allows measurement of fractional flow reserve (FFR). The latter has received a class I indication with level of evidence A according to the most recent European guidelines on myocardial revascularization for the assessment of angiographically moderate coronary lesions. The present document has the following objectives: 1) to summarize the theoretical basis of FFR; 2) to provide a guideline for vasodilator therapy; 3) to summarize scientific evidence supporting FFR; 4) to provide a model of health economy evaluation focusing on resource sparing associated with the use of FFR.