Pivotal work by DeBruyne, Pils and colleagues in the 90's convincingly showed that pressure derived measurements, called FFR, from the coronary artery during a cardiac catheterization, more accurately identify stenoses that would cause ischemia compared to visual assessment alone. A strategy of FFR guided coronary stenting with drug eluting stents significantly improved outcomes and reduced costs compared to visual assessment alone (FAME trial). Deferring treatment based on FFR has been shown to be safe (DEFER Trial). FFR has excellent sensitivity and specificity. A FFR of <=0.80 was used as this identified ischemia causing lesions 90% of the time. Therefore, the concept of FFR guided percutaneous revascularisation and treatment deferral has a robust evidence base to support it.