The routine use of physiology to guide revascularisation is unacceptably low. To improve adoption iFR has been introduced. This index is based on established physiology, can be measured within seconds, does not require hyperaemic agents and uses existing pressure wire technology. Importantly, it has the potential to extend the role of physiology by permitting accurate assessment of vessels with diffuse disease or tandem lesions. The unique characteristics of iFR physiology combined with modern imaging opens the potential of virtual PCI: for the first time allowing physiology to tell us not only if we need a stent but where and therefore how to stent to get the best outcomes for our patients.