Incidence of and mortality from cardiovascular diseases have been studied in a cohort of 12,210 workers first employed at one of the main plants of the Mayak nuclear facility during 1948–1958 and followed up to 31 December 2000. Information on external γ-ray doses is available for virtually all of these workers (99.9%); the mean total γ-ray dose (±SD) was 0.91 ± 0.95 Gy (99% percentile 3.9 Gy) for men and 0.65 ± 0.75 Gy (99% percentile 2.99 Gy) for women. In contrast, plutonium body burden was measured for only 30.0% of workers; among those monitored, the mean cumulative liver dose from plutonium alpha exposure (± SD) was 0.40 ± 1.15 Gy (99% percentile 5.88 Gy) for men and 0.81 ± 4.60 Gy (99% percentile 15.95 Gy) for women. A total of 3751 cases of ischemic heart disease (IHD), including 683 cases of acute myocardial infarction (AMI), and 1495 IHD deaths, including 338 AMI deaths, were identified in the study cohort during the follow-up period. Having adjusted for non-radiation factors, there were statistically significant increasing trends with both total external γ-ray dose and internal liver dose in IHD incidence. The trend with internal dose was weaker and was not statistically significant after adjusting for external dose, whereas the external dose trend was little changed after adjusting for internal dose. The trend with external dose in IHD mortality was not statistically significantly greater than zero but was consistent with the corresponding trend in IHD incidence. The estimated trend in IHD mortality with internal dose was lower and was not statistically significant once adjustment was made for external dose. There was a statistically significantly increasing trend in AMI incidence but not AMI incidence with external dose. The risk estimates for IHD in relation to external radiation are generally compatible with those from other large occupational studies and the Japanese A-bomb survivors.