Despite being as common as an acute myocardial infarction in the emergency department, the diagnostic criteria and the therapeutic guidelines for heart failure treatment are much less well defined. Thanks to the recently published guidelines of the European Society of Cardiology (ESC) the diagnosis of acute heart failure syndromes (AHFS) is now better standardized. The ESC distinguishes between six AHFS: (I) acute decompensated chronic heart failure, (II) acute heart failure with hypertension/hypertensive crisis, (III) acute heart failure with pulmonary edema, (IV) cardiogenic shock, (V) high-output failure, and (VI) right-sided acute heart failure. To distinguish between these entities in a clinical setting, a well-structured clinical examination is of paramount importance. Signs of peripheral hypoperfusion and congestion/fluid overload need to be recognized rapidly. These two clinical parameters permit the assessment of the patient based on the Clinical Severity Classification. Further diagnostic work-up should include chest X-ray, echocardiography, clinical chemistry, and blood gas analysis. The invasive coronary angiography is only beneficial in the context of an acute ST elevation myocardial infarction or NSTEMIs with persistent symptoms of angina. In all other cases cardiac catheterization should be deferred until the patient is recompensated. Diagnostic algorithms help to maintain a high standard in clinical diagnosis and improve the safety and efficacy of subsequent therapeutic interventions.