Aims, This study was performed to assess the differences in culprit plaque composition between patients with and without pre-infarction angina (PA) by using spectral analysis of intravascular ultrasound (IVUS) radiofrequency (RF) data. Methods and results, Of 57 patients consecutively admitted to our institution with acute myocardial infarction, pre-intervention IVUS RF data of culprit plaques were obtained and analysed in 35 patients after percutaneous aspiration thrombectomy. Among the 35 patients, 21 patients had PA. Culprit plaques of patients without PA consisted of a higher percentage of the necrotic core component than those with PA (minimum lumen area [MLA]) site, 21.2+/-8.9% versus 9.9+/-9.8%, p=0.0015; entire culprit lesion, 18.9+/-6.3% versus 12.0+/-9.6%, p=0.023). In contrast, culprit plaques of patients with PA contained a higher percentage of the fibrofatty component than those without PA (MLA site, 21.0+/-12.0% versus 11.5+/-7.6%, p=0.013; entire culprit lesion, 16.8+/-7.9% versus 12.1+/-5.5%, p=0.062). There was no significant difference in quantitative parameters between the patients with and without PA. Conclusions, Culprit plaques of patients with PA were different from those without PA. Plaque composition may play an important role in the occurrence of PA.