This is a prospective single center study that will enroll 200 patients undergoing clinically indicated cardiac catheterization for stable ischemic heart disease or unstable chest pain, who are also undergoing NIRS-IVUS direct coronary imaging of a culprit lesion based on routine clinical indications. The NIRS/IVUS catheter uses near-infrared light (red laser light) and intravascular ultrasound (sound waves) to identify fatty plaques in the coronary artery. Standard angiography, near-infrared spectroscopy (NIRS) and intravascular ultrasound (IVUS) are three widely used clinical methods to image narrowing within the coronary arteries at the time of cardiac catheterization.