The objective of the EuroHeart Failure Survey II (EHFS II) was to assess patient characteristics, aetiology, treatment, and outcome of acute heart failure (AHF) in Europe in relation to the guidelines on the diagnosis and treatment of AHF published by the European Society of Cardiology. Patients hospitalized for AHF were recruited by 133 centres in 30 European countries. Three thousand five hundred and eighty patients were entered into the database by the end of August 2005. Mean age was 70 years, and 61% of patients were male. New-onset AHF (de novo AHF) was diagnosed in 37%, of which 42% was due to acute coronary syndromes (ACS). Clinical classification according to the guidelines divided AHF patients into (i) decompensated HF (65%), (ii) pulmonary oedema (16%), (iii) HF and hypertension (11%), (iv) cardiogenic shock (4%), and (v) right HF (3%). Coronary heart disease, hypertension, and atrial fibrillation were the most common underlying conditions. Arrhythmias, valvular dysfunction, and ACS were each present as precipitating factor in one-third of cases. Preserved left ventricular ejection fraction (> or =45%) was observed in 34%. Valvular disorders were common, especially mitral regurgitation (MR) which was reported on echocardiography in 80% of patients. Median length of stay was 9 days, and in-hospital mortality 6.7%. At discharge, 80% of patients were on angiotensin-converting enzyme-inhibitors or angiotensin receptor blockers, whereas 61% were taking beta-blocker medication. Decompensated HF is the most common clinical presentation of AHF patients. More than one-third of AHF patients do not have a previous history of HF, and new-onset HF is often caused by ACS. Preserved systolic function is found in a substantial proportion of the patients. The prevalence of valvular dysfunction is strikingly high and contributes to the clinical presentation. The EHFS II on AHF verified that the use of evidence-based HF medication was well adopted to clinical practice.