Flu infection may make cardiovascular disease (e.g. heart attack, stroke) and associated death more likely, and flu vaccination may reduce this risk. We included randomised studies comparing people receiving flu vaccine with those receiving no vaccine (placebo or no treatment). For this review update, we found eight trials studying 12,029 participants. Four of these studies examined patients with known heart disease (1682 participants), and the other four focused on the general population or elderly people (10,347 participants). The general population studies reported cardiovascular disease outcomes as part of their safety analyses, but the numbers of cases were too few to allow a judgement on whether flu vaccination was protective in these populations, and no differences were seen between groups. Overall, studies in people with heart disease suggest that flu vaccination may reduce death as a result of cardiovascular disease and may reduce combined cardiovascular disease events (such as heart attacks, strokes, necessity for bypass operations, etc.). However, these studies were small and had some risk of bias, so larger studies of better quality are needed to confirm the results.