The current standard of invasive coronary stenosis assessment is the hyperemic translesional pressure ratio, widely known as the fractional flow reserve (FFR). FFR is the ratio of distal post-stenotic pressure (Pd) to the aortic pressure (Pa) during pharmacologically-induced maximal flow stimulation usually with adenosine. In the last decade in order to simplify workflow and reduce the side effects of adenosine, clever investigators demonstrated that a resting diastolic sub-cycle pressure measurement, the instantaneous wave-free pressure ratio (iFR), is non-inferior to FFR in low risk coronary artery disease (CAD) patients and that other non-hyperemic pressure ratios (NHPRs) are numerically and clinically equivalent to iFR for the limited outcome data available.