Fractional flow reserve (FFR) is an evidence-based diagnostic tool of physiological significance of coronary artery stenosis in patients with stable coronary artery disease (CAD). Due to microvascular dysfunction in acute coronary syndrome (ACS), information obtained from FFR assessment could be less reliable and, thus, its clinical role remains controversial. Indeed, results of currently published studies are essentially discrepant. Only a few randomized clinical trials have been performed showing the efficacy of FFR-guided percutaneous coronary intervention in ACS. Consequently, its role in acute scenarios remains substantially understudied. Herein, is presented the current state of knowledge regarding FFR use in ACS setting. (Cardiol J 2017; 24, 4: 426–435
