IMPORTANCE: Influenza is associated with an increased risk of cardiovascular events, but to our knowledge, few studies have explored the temporal association between influenza activity and hospitalizations, especially those caused by heart failure (HF). OBJECTIVE: To explore the temporal association between influenza activity and hospitalizations due to HF and myocardial infarction (MI). We hypothesized that increased influenza activity would be associated with an increase in hospitalizations for HF and MI among adults in the community. DESIGN, SETTING, AND PARTICIPANTS: As part of the community surveillance component of the Atherosclerosis Risk in Communities (ARIC) study, a population-based study with hospitalizations sampled from 4 US communities, data were collected from 451 588 adults aged 35 to 84 years residing in the ARIC communities from annual cross-sectional stratified random samples of hospitalizations during October 2010 to September 2014. EXPOSURES: Monthly influenza activity, defined as the percentage of patient visits to sentinel clinicians for influenza-like illness by state, as reported by the Centers for Disease Control and Prevention Surveillance Network. MAIN OUTCOMES AND MEASURES: The monthly frequency of MI hospitalizations (n = 3541) and HF hospitalizations (n = 4321), collected through community surveillance and adjudicated as part of the ARIC Study. RESULTS: Between October 2010 and September 2014, 2042 (47.3%) and 1599 (45.1%) of the sampled patients who were hospitalized for HF and MI, respectively, were women and 2391 (53.3%) and 2013 (57.4%) were white, respectively. A 5% monthly absolute increase in influenza activity was associated with a 24% increase in HF hospitalization rates, standardized to the total population in each community, within the same month after adjusting for region, season, race/ethnicity, sex, age, and number of MI/HF hospitalizations from the month before (incidence rate ratio, 1.24; 95% CI, 1.11-1.38; P