Background The purpose of this study was to assess temporal trends in clinical characteristics, treatments, quality indicators, and outcomes for heart failure (HF) hospitalizations. Methods Characteristics, treatments, quality measures, and inhospital outcomes were measured over 12 consecutive quarters (January 2002 to December 2004) using data from 159 168 enrollments from 285 ADHERE hospitals. Results Baseline characteristics were similar or showed only modest changes, and severity of illness by logistic regression was unchanged over all 12 quarters. Inhospital treatment changed significantly over time with inotrope use decreasing from 14.7% to 7.9% ( P < .0001). Discharge instructions increased 133%; smoking counseling, 132%; left ventricular function measurement, 8%; and β-blocker use, 29% (all P < .0001). Clinical outcomes improved over time, including need for mechanical ventilation, which decreased 5.3% to 3.4% (relative risk 0.64, P < .0001); length of stay (mean), 6.3 to 5.5 days; and mortality, 4.5% to 3.2% (relative risk 0.71, P < .0001). Conclusions Over a 3-year period, demographics and clinical characteristics were relatively similar, but significant changes in intravenous therapy, enhancements in conformity to quality-of-care measures, increased administration of evidence-based HF medications, and substantial improvements in inhospital morbidity and mortality were observed during hospitalization for HF.