According to several large studies, there are significant dose-related increases after radiation exposure in the incidence of cardiovascular diseases, such as stroke or myocardial infarction, and circulatory disease/dysfunction, including chronic kidney disease. However, no basic in vivo studies have described the detailed pathological and/or molecular features or mechanisms underlying the development of radiation-induced cardiovascular diseases. In “a comprehensive dose evaluation project concerning animals affected by the FNPP accident” (Affected Animal Project), our group focused on the histopathological findings of the cardiovascular system in Japanese macaques with persistent whole-body exposure to low-dose-rate radiation in the area affected by the Fukushima Daiichi Nuclear Power Plant (FNPP) accident. We found that none of the 320 macaques affected by the accident showed any histopathologically severe atherosclerotic changes or overt myocardial infarctions. Furthermore, 12 macaques (12/320; 3.75%) revealed very mild intimal thickening in the relatively peripheral small coronary arteries, and in one case, the stenotic rate was only as high as approximately 15%. It may be too early to detect any significant findings of cardiovascular disease, such as atherosclerosis, in radiation-exposed Japanese macaques. Therefore, we propose that this project be continued as consecutive, multidisciplinary investigations, including molecular analyses, over the next 15–30 years.