Electron beam computed tomographic studies have demonstrated that the extent of intracoronary calcium is related to risk of coronary events. This study was performed to gain further insight into the distribution of focal calcifications and their relation to the site of plaque rupture within the culprit artery in consecutive patients(n=60) with acute myocardial infarction(AMI) using intravascular ultrasound imaging. Calcifications in the culprit lesion and adjacent segments were classified and counted according to their arc(< 45°, 45°to 90°, 90°to 180°, >180°), length(< 1.5, 1.5 to 3.0, 3.0 to 6.0, >6.0 mm), and dispersion(number of spots per millimeter). Calcifications at the edge of a visible rupture or ulceration were considered related to the AMI. Compared with adjacent proximal and distal segments, the culprit lesion contained more calcified spots per millimeter(0.14, 0.10, and 0.21, respectively, p< 0.05). Small calcified spots(arc< 45°, length< 1.5 mm) were more common(p< 0.05). Plaque rupture or ulceration was manifest in 31 culprit lesions(52%), 14(45%) of which contained focal calcifications. These calcified spots extended more often to 90°to 180°of the vessel circumference and were more often of moderate length(3 to 6 mm) compared with culprit lesions without visible plaque rupture(p< 0.05). In conclusion, culprit lesions in patients with AMI contain more and smaller calcifications compared with adjacent segments. Calcifications related to plaque rupture appear to be larger and extend over a wider arc compared with these calcified spots. Those larger calcified spots may play a role in plaque instability in a subgroup of lesions. Electron beam computed tomographic studies have demonstrated that the extent of intracoronary calcium is related to risk of coronary events. This study was performed to gain further insight into the distribution of focal calcifications and their relation to the site of plaque rupture within the culprit artery in consecutive Calcifications in the culprit lesion and adjacent segments were classified and sorted according to their arc (<45 °, 45 ° to 90 °, 90 ° to 180 ° ,> 180 °), length (<1.5, 1.5 to 3.0, 3.0 to 6.0,> 6.0 mm), and dispersion (number of spots per millimeter). Calcifications at the edge of a visible rupture or ulceration were considered related to the AMI . Compared with adjacent proximal and distal segments, the culprit lesion contained more calcified spots per millimeter (0.14, 0.10, and 0.21, respectively, p <0.05) Small calcified spots (arc <45 °, length <1.5 mm) (p < 0.05). Plaque rupture or ulceration was manifest in 31 culprit lesions (52%), 14 (45%) of which contained focal calcifications. These calcified spots extended more often to 90 ° to 180 ° of the vessel circumference and were more often of Moderate length (3 to 6 mm) compared with culprit lesions without visible plaque rupture (p <0.05). In conclusion, culprit lesions in patients with AMI contain more and smaller calcifications compared with adjacent segments. Calcifications related to plaque rupture appear to be larger and extend extend a more arc compared with these calcified spots. Those larger calcified spots may play a role in plaque instability in a subgroup of lesions.