Compared to anatomical assessment by coronary angiography, physiological assessment can more effectively guide management decisions in distinguishing an intermediate coronary stenosis that requires revascularization or medical therapy. Fractional flow reserve (FFR) is an established invasive pressure-wire based index for determination of the functional severity of a coronary stenosis. Several previous randomized studies have demonstrated that patients with stable coronary artery disease (CAD) can benefit from FFR-guided treatment strategy over angiography-guided treatment strategy [ ]. Recently, the instantaneous wave-free ratio (iFR) that does not need to induce hyperemia has been introduced as an alternative to FFR. Two large randomized controlled trials (RCT) of DEFINE-FLAIR [ ] and iFR-SWEDEHEART [ ] have shown that iFR-guided strategy is non-inferior to FFR-guided strategy for revascularization therapy in CAD patients. Therefore, the current guidelines recommend the use of FFR or iFR to guide revascularization with percutaneous coronary intervention (PCI) in patients with angiographically intermediate stenoses (Class I, Level of Evidence: A).