Introduction
The functional assessment of coronary stenosis is crucial for the appropriate management of coronary artery disease (CAD). Introduced over 30 years ago, Fractional Flow Reserve (FFR) emerged as a reliable method to assess the significance of intermediate-grade coronary lesions. More recently, the development of instantaneous wave-free ratio (iFR) and other non-hyperemic pressure ratios (NHPRs) has offered new alternatives that do not require the induction of hyperemia. This review discusses the concepts and features of FFR and NHPRs, highlighting their similarities and differences.