Fractional Flow Reserve or FFR is a guide wire-based procedure that can accurately measure blood pressure and flow through a specific part of the coronary artery. FFR is done through a standard diagnostic catheter at the time of a coronary angiogram. The measurement of Fractional Flow Reserve has been shown useful in assessing whether or not to perform angioplasty or stenting on "intermediate" blockages.

Measurements are taken by placing the wire across the lesion of interest and inducing a state of maximum blood flow, thereby allowing the physician to determine if the narrowing is tight enough to cause ischemia. FFR is defined as the ratio of maximal blood flow in a stenotic (narrowed) artery to normal maximal flow, expressed as a fraction of thenormal blood flow in an artery compared to the maximum achievable blood flow in the same artery.