Influenza Vaccine to Effectively Stop Cardio Thoracic Events and Decompensated heart failure (INVESTED) I s a multi-center, randomized, double blind, active-control trial of high dose influenza vaccine compared to standard dose influenza vaccine for three seasons in adult participants with a history of myocardial infarction or heart failure. The primary outcome measure is the composite of death or cardiopulmonary hospitalizations, and secondary outcomes include composite of cardiopulmonary death or cardiopulmonary hospitalization, all-cause death or all-cause hospitalization, all-cause death or cardiovascular hospitalization, cardiopulmonary death, and all cause death. Background: The substantial number of individuals in North America with myocardial infarction or heart failure (HF) are at high risk for influenza infection and associated morbidity, mortality and increased health care costs despite annual influenza vaccination. Higher dose of vaccine is approved for use in older adults but not in patients with heart failure. Antibody-mediated immunity contributes to vaccine-induced protection from influenza illness. Preliminary data: Our research group has shown in a meta-analysis that influenza vaccine reduces the risk for cardiovascular events and has also demonstrated reduced antibody titers to influenza vaccination in patients with HF. Additionally, we've shown in a pilot study that double dose influenza vaccine resulted in increased titers and was well tolerated. Methods: A multi-center, randomized, double blinded randomized trial will be conducted with 4650 patients assigned to the standard dose vaccine dose and 4650 patients to high dose influenza vaccine. The primary outcome measure is the composite of death or cardiopulmonary hospitalization, assessed at the end of each influenza season. Secondary outcomes will include the composite of death or cardiovascular hospitalizations, death or all-cause hospitalizations, and mortality. The study will also examine associations between geometric mean antibody titers and risk for death or cardiopulmonary hospitalizations. Significance: A positive trial may be able to provide crucial information to infom health care policy regarding optimal influenza vaccination dosing among individuals with high risk cardiovascular disease.