Objective: To determine the clinical and prognostic differences between patients with heart failure who had preserved or deteriorated systolic function, defined as a left ventricular ejection fraction of > 50% or < 50%, respectively, within two weeks of admission to hospital. Methods: The records of 229 patients with congestive heart failure were studied. There were 95 women and 134 men, mean (SD) age 66.7 (11.7) years, who had been admitted to a cardiology department for congestive heart failure in the period 1991 to 1994, and whose left ventricular systolic function had been evaluated echocardiographically within two weeks of admission. Data were collected on the main clinical findings, supplementary investigations, treatment, and duration of hospital admission. Follow up information was obtained in the spring of 1998 by searching the general archives of the hospital and by a telephone survey. Results: Left ventricular systolic function was preserved in 29% of the patients. The preserved and deteriorated groups differed significantly in the sex ratio (more women in the preserved group) and in the presence of a third heart sound, cardiomegaly, alveolar oedema, ischaemic cardiomyopathy, and treatment with angiotensin converting enzyme (ACE) inhibitors (all more in the deteriorated group). There were no significant differences in age, New York Heart Association functional class, rhythm disturbances, left ventricular hypertrophy, treatment with drugs other than ACE inhibitors, or survival. In the group as a whole, the survival rates after three months, one year, and five years were 92.6%, 80%, and 48.4%, respectively. Conclusions: In view of the unexpectedly poor prognosis of patients with congestive heart failure and preserved left ventricular systolic function, controlled clinical trials should be carried out to optimise their treatment.