Atherosclerotic disease involving coronary artery bifurcations continues to be a perplexing and difficult subject. This is nowhere more evident than in their physiological assessment. With a coronary bifurcation, there are three arterial segments to evaluate: 1) the main branch proximal to the bifurcation (MB-proximal); 2) the main branch distal to the bifurcation (MB-distal); 3) the side branch (SB). This arrangement is the anatomic basis for the Medina classification, a system proven useful in understanding bifurcation lesions and their treatment (Fig. 1) [1]. However, the multiple possible permutations of lesion anatomy, along with frequently encountered difficulties in manipulating guidewires and pressure-wires into the side branch, make physiological assessment of bifurcation lesions more challenging, and therefore less often performed.