AbstractAssessment of relationship between the angiographic stenosis severity and the coronary blood flow is complex. Coronary angiography has many limitations that may impair the judgment of stenosis severity and then affect decision-making regarding intervention. Myocardial perfusion imaging by single-photon emission tomography (MPI-SPECT) is used for a long time to help clinical decisions of interventions, but has limitations, such as issues with identification of extensive coronary artery disease (CAD). Fractional flow reserve (FFR) is a gold standard index for investigating the physiological significance of a coronary stenosis. The instantaneous wave-free ratio (iFR) is a hyperemia-free measurement and easier method to achieve physiological assessment to measure the severity of coronary stenosis. We present a case of multivessel coronary artery disease (MVCAD) patient who was treated with iFR-guided percutaneous coronary intervention (PCI) and emphasize the importance of physiological assessment in PCI. A 63-year-old male with multiple cardiovascular risk factors came to our center with chief complaint of stable angina since 1 year. He underwent MPI-SPECT and the result showed 2.5% of ischemia burden. Coronary angiography showed MVCAD. Surgical conference decided to do PCI. iFR-guided PCI was performed in this case. Our case highlights the importance of iFR as an important cardiology–physiology-based tool as a guide in management decisions for MVCAD. iFR as an alternative approach to physiological study is noninferior compared with FFR-guided PCI.