Background The elderly make up the majority of patients with heart failure (HF), but information on this segment of the HF population is lacking because clinical trials typically enroll younger patients and population-based studies lack clinical detail. We sought to describe a contemporary national sample of elderly patients with HF and to examine the sample for age-related trends in clinical characteristics. Methods We studied the charts of 800 Medicare patients per state who were hospitalized with a principal diagnosis of HF between April 1998 and March 1999. There were 34,587 patients in the sample after exclusion of patients who were <65 years old, repeat discharges, discharges to another acute care facility or against medical advice, or receiving long-term hemodialysis. Results Comorbidity was common. About one third of patients had chronic obstructive pulmonary disease, about 40% had diabetes, more than half had coronary heart disease, and more than half had a history of hypertension, but comorbidity rates declined with age. Left ventricular ejection fraction was <40% in only 50.4% of patients in whom it was assessed. Associated laboratory abnormalities were relatively constant across the age spectrum, but renal insufficiency was more common with advancing age. The likelihood that patients were in long-term care facilities before admission rose quite steeply with age. Conclusions Elderly patients with HF are a heterogeneous group and appear to differ substantially from patients enrolled in clinical trials. Evidence-based guidance for treatment in the context of multiple comorbid conditions, poor renal function, HF with preserved left ventricular systolic function, and residence in long-term care facilities is urgently needed. (Am Heart J 2002;143:412-7.)