Traditionally, the severity of a blockage (stenosis) in a coronary artery has been determined by visual angiographic assessment of the diameter of the artery at the level of a blockage compared to a normal healthy area of the same artery. With the advent of invasive physiological testing to assess coronary blood flow, multiple clinical trials have demonstrated a clinical benefit to a physiology-guided percutaneous coronary intervention (PCI) approach. However, despite this and the potential for significant variation in the interpretation of coronary artery stenosis severity by visual angiography alone to guide PCI, invasive physiologic indices remain significantly under-utilized. The purpose of this study is to investigate the physiologic significance of coronary lesions deemed angiographically severe by visual estimation that are planned for PCI. The investigators plan to perform blinded physiologic assessment pre and post PCI. The primary aim of the study is to determine whether a subset of lesions visually estimated as severe by angiography treated with stent placement/PCI may in fact not be physiologically significant when assessed invasively, and thus PCI could safely be deferred in these patients. A secondary aim is to evaluate physiologic assessment post PCI to detect residual ischemia that could be utilized to optimize stent placement.