Background To examine age-specific differences in the frequency and impact of cardiac and non-cardiac conditions among patients aged 65 years and older hospitalized with acute myocardial infarction (AMI). Methods Study population consisted of 3863 adults hospitalized with AMI at 11 medical centers in central Massachusetts on a biennial basis between 2001 and 2011. The presence of 11 chronic conditions (five cardiac and six non-cardiac) was based on the review of hospital medical records. Results Participants' median age was 79 years, 49% were men, and had an average of three chronic conditions (average of cardiac conditions: 2.6 and average of non-cardiac conditions: 1.0). Approximately one in every two patients presented with two or more cardiac related conditions whereas one in every three patients presented with two or more non-cardiac related conditions. The most prevalent chronic conditions in our study population were hypertension, diabetes, heart failure, chronic kidney disease, and peripheral vascular disease. Patients across all age groups with a greater number of previously diagnosed cardiac or non-cardiac conditions were at higher risk for developing important clinical complications or dying during hospitalization as compared to those with 0–1 condition. Conclusions The prevalence of multimorbidity among older adults hospitalized with AMI is high and associated with worse outcomes that should be considered in the management of this vulnerable population.