Prospective, cross-sectional study of observation of all patients admitted to the Internal Medicine service for one year, adults, with primary or secondary diagnosis of acute heart failure (HF). The aim of the study was to characterize this population. 118 patients (mean age 84 ± 7.9 years). 81.4% had decompensated chronic HF. On admission: 84.6% were class III and IV (NYHA); 60.5% had preserved ejection and diastolic dysfunction. Those with functional class III-IV had lower ejection fractions (59.56 vs 65.97, p <0.01). Infection was the most frequent cause of exacerbation, except for HF “again”. The ID correlates independently of the presence of anemia with mortality, as well as the clinical severity and LVEF (p <0.05). The overall mortality was 52.2%. Mortality is higher in those with a previous history of cardiovascular disease. Patients with HF “again” had similar in-hospital mortality, but less after discharge. Thus, patients admitted to an internal medicine service are mostly elderly women, with pluripathology, with chronic acute HF due to infection and with high morbidity. Therefore, it is extremely important to compensate this patient and monitor closely after discharge.