Influenza is a major cause of morbidity and mortality. Influenza epidemics lead to an increase in pneumonia–influenza deaths and a considerable increase in death due to cardiovascular disease (CVD). The effects of influenza infection on CVD are just being recognized. Many cases of myocardial infarctions (MI) are preceded by an upper respiratory infection. Influenza vaccination has been associated with a remarkable reduction in the risk of secondary MI, sudden cardiac arrest, stroke, and hospitalization for cardiac causes. A pilot, randomized clinical trial has shown a marked reduction in cardiovascular death in patients with acute MI and those undergoing percutaneous coronary interventions. Influenza may trigger acute coronary syndromes by destabilizing the already-present atherosclerotic vulnerable plaques. Infected apoE-deficient mice demonstrate a marked increase in inflammation in their atherosclerotic plaques. New clinical trials are needed to identify special groups (e.g., patients with asymptomatic CVD or with multiple CVD risk factors), which may benefit from vaccination and may call for expansion of current guidelines. © 2003 Elsevier B.V.