Angiographic studies in 3 patients illustrate the physiological adaptability of internal mammary artery (IMA) grafts. Intact vascular smooth muscle permits the IMA grafts to retain a flexible caliber and a blood flow dictated by myocardial demands in the distribution of the grafted coronary artery. This physiological nature may be one of the reasons for their continued patency regardless of whether they are grafted to large or small coronary arteries. Further, this adaptable behavior permits use of the IMA even if its distal lumen is smaller than that of the recipient coronary artery, provided the anastomosis can be safely performed and the demand for flow is present.