There is no linear relationship between the percentage of coronary narrowing and its functional significance, as demonstrated more than 20 years ago. This observation was later confirmed in studies that compared coronary artery imaging to fractional flow reserve (FFR) measurement. In a subanalysis of data from the FAME trial, FFR was >0.8 (i.e. the stenosis was considered to be functionally nonsignificant) for 63% of stenoses that had been visually estimated to be “intermediate” (i.e. 50%–70% of vessel diameter) and for 20% of severe stenoses (70%–90% of vessel diameter). A non-invasive method that produces reliable information on both the anatomy and the functional significance of coronary artery stenosis would decrease the need for invasive coronary angiography (ICA). Ideally, ICA should be performed only for patients requiring percutaneous angioplasty.