The effects of balloon angioplasty (BA) on plaque distribution remain incompletely documented. In 20 patients with unstable angina pectoris, intravascular ultrasound gray scale and radiofrequency analyses were performed before and after BA. Composition of the plaque was 61% fibrotic tissue, 15% fibrofatty tissue, 15% necrotic tissue, and 7% dense calcium tissue. After BA, 35% of lumen enlargement was due to an increase in total vessel area and 65% to a significant decrease in plaque area. This resulted from a longitudinal redistribution of the tissue toward the reference segments. Radiofrequency analysis showed that the fibrous and fibrofatty tissues were able to redistribute longitudinally, whereas calcium remained at the same level. A third of necrotic tissue was lost after BA. In conclusion, in unstable plaques, BA resulted in a longitudinal redistribution of fibrotic and fibrofatty tissues and disappearance of 1/3 of necrotic tissue.