Purpose of Review: Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) have emerged as the invasive diagnostic tools of choice for hemodynamic assessment of the severity of CAD (coronary artery disease). We sought to comprehensively review the evidence on the utility of hemodynamic assessment of the coronary stenoses after percutaneous coronary intervention (PCI) using FFR/iFR, mechanisms of positive post-PCI iFR/FFR, and the clinical impact of significant residual ischemia. Recent Findings: The evidence on the utility of the post-PCI hemodynamic assessment has accumulated over the last few years. The post hoc analysis from the FAME 1 and FAME 2 data shows that higher post-PCI FFR is associated with better symptomatic improvement and lower event rate with larger increase in delta FFR (∆ FFR: post-PCI FFR – pre-PCI FFR). Unlike pre-PCI FFR, a consensus has not been established on the optimal value of post-PCI FFR, though multiple studies point toward better clinical outcomes with higher post-PCI FFR and larger ∆ FFR. Summary: Visual assessment of adequate stent apposition by coronary angiography is insufficient in evaluating for residual ischemia. The hemodynamic evaluation of residual ischemia by post-PCI FFR/iFR yields clinically relevant data and allows for appropriate post PCI optimization.