The 2-dimensional silhouette image provided by coronary angiography has well-recognized limitations. Angiographic images do not accurately represent the true complexity of the luminal morphology in coronary disease and give no indication of the functional influence of luminal changes on coronary blood flow. These limitations are more pronounced in angiographically intermediate stenoses and in patients in whom there is a clear discrepancy between the clinical picture and angiographic findings. In such cases there is often poor concordance between the estimated percentage angiographic stenosis and the corresponding intravascular ultrasound image or noninvasive functional data. The validation and clinical availability of robust and accurate physiologic indices, which can be used as an adjunct to diagnostic angiography in the cardiac catheterization laboratory, have been pivotal in promoting ischemia-driven coronary revascularization. Deferral or revascularization based on such physiologic indices is associated with improved clinical outcome as well as more favorable health economic data. Although there are several clinical indices, fractional flow reserve remains the "gold standard," with indications for physiologic assessment of angiographic intermediate stenoses, including left main stem stenoses and ostial disease as well as serial lesions. The availability of such indices is an important step in streamlining management of patients undergoing cardiac catheterization by allowing routine provision of an "all-in-one" ischemia-driven revascularization service.