For over thirty years, cardiologists and technologists have been looking up at the cardiac cath lab angiography screen and asking each other, “What do you think?” “What should we do about that lesion?” “Is this stenosis severe enough for the patient to benefit from intervention?” These questions were followed with multiple views and contrast injections. Unfortunately, the additional radiation exposure and contrast would rarely yield a definitive answer to these questions. However, thanks to advances in interventional cardiology, physicians who practice evidence-based medicine have at their disposal two technologies. These technologies can provide definitive answers to questions of lesion significance and direct appropriate medical and interventional therapies. The technologies that offer this supporting evidence are Fractional Flow Reserve (FFR) and Intravascular Ultrasound (IVUS). FFR can determine if a suspect lesion is limiting the flow of blood to the heart muscle, causing ischemia; while IVUS can differentiate the disease pathology, plaque burden and true cross-sectional area of the culprit lesion. These tools serve as guides in interventional therapy, determining stent expansion and apposition in an effort to achieve optimal patient results.