Previous pathological studies demonstrated that the atherosclerotic coronary artery enlarges in response to developing atherosclerotic plaque. To clarify this phenomenon of coronary arterial remodeling, 24 segments of the left anterior descending artery were studied with intravascular ultrasound imaging. The luminal area and vessel area (area bounded by the echolucent zone) were measured by planimetry, and the percentage plaque area was calculated. Vessel area was correlated with plaque area (y = 12.3 + 0.72, r = 0.54, p < 0.001). When the 24 coronary segments were divided into two categories according to the percentage plaque area, there was no correlation between plaque area and lumen area in the coronary segment with less than 40% plaque area (n = 14, r = 0.20, p = NS) or less than 30% plaque area (n = 9, r = 0.18, p = NS). However, there was a correlation between plaque area and lumen area in the coronary segments with greater than 40% plaque area (n = 10, y = 22.1-0.27x, r = -0.82, p < 0.01). The correlation was somewhat better in cases with greater than 30% plaque area (n = 15, y = 22.5-0.28x, r = -0.89, p < 0.0001). Intravascular ultrasound imaging demonstrates the phenomenon of coronary arterial remodeling in vivo, which indicates that human coronary artery enlarges in response to increasing plaque area until the plaque occupies 30% of the vessel area. However, if the plaque occupies more than 30%, an increase in plaque area leads to a decrease in lumen area. Therefore, the phenomenon of coronary arterial remodeling is a compensatory mechanism to prevent luminal narrowing in the early stage of human coronary atherosclerosis.