Heart failure is a difficult disease to define. It is easy to recognise heart failure in its moderate/severe version where the patient has pronounced symptoms and signs accompanied by echocardiographic evidence of left ventricular (LV) systolic dysfunction.1 However, the problem of defining heart failure arises in its milder forms where patients may complain of dyspnoea but do not have echocardiographic evidence of LV systolic dysfunction. The complexities of what represents heart failure are illustrated in fig 1 but space precludes a detailed discussion of the definition of heart failure. Figure 1 The various subcategories of heart failure. To overcome the various difficulties in defining heart failure, the European Society of Cardiology (ESC) has developed guidelines for the diagnosis of heart failure.2 However, like all statements which are meant to define the undefinable, there is a certain deliberate vagueness about them. For example, they do not specify what they mean by cardiac dysfunction. Does an elderly lady whose echocardiogram meets criteria for “diastolic dysfunction” and who has swollen ankles have heart failure, even if she has no breathlessness or fatigue? Despite this caveat, the ESC guidelines have clarified the situation, even if one can still point to isolated patients who remain ambiguous with the ESC definition.#### European Society of Cardiology guidelines for the diagnosis of heart failure At a more pragmatic level, the clinician who is faced with a patient with suspected heart failure should try to answer two major questions: 1. : Are the patient's symptoms cardiac in origin? 2. : If so, what kind of cardiac disease is producing these symptoms? In order to answer these questions, the clinician goes through the standard process of assessing the patient's symptoms, …