The coronary arteries are difficult to image noninvasively because of the small size of even the larger vessels (2–4 mm), the tortuous course of the vessels along the epicardial surface, and physiologic movement related to cardiac and respiratory motion. Excellent temporal resolution is required for high-quality images of the coronary arteries and to assess indices of left ventricular function such as ejection fraction and wall motion. Whereas diagnostic invasive coronary angiography has reached a high state of development over the past three decades, noninvasive coronary imaging has progressed more slowly.