Appearances can deceive: even brave hearts can fail.

The enigma faces us every day and we still do not know how to define or manage it. Patients develop the typical signs and symptoms of heart failure although they apparently have “normal” left ventricular systolic function. The syndrome occurs both acutely and chronically and is responsible for approximately half of the heart failure epidemic.1 The terminology is the subject of debate. There is consensus that patients with “diastolic heart failure” or “heart failure with preserved left ventricular function” tend to be older and more frequently female with a history of hypertension. The rates of other common co-morbidities appear to be similar. Prognosis is generally as poor as in patients with systolic dysfunction. Given the paucity of studies assessing the incidence and prevalence of this common condition, the paper “Differences between patients with a preserved and a depressed left ventricular function: a report from the EuroHeart Failure Survey” by Lenzen et al., published in this issue, is a welcome contribution. The report compares the demographic differences between patients with reduced ejection fractions and patients with preserved left ventricular function based on data from the EuroHeart Failure survey.3 The reported data helps us to understand some of the similarities and differences between the patient characteristics of these two groups. The red herring may be our traditional dependence on the time-honoured concept of the ejection fraction, and the relatively arbitrary thresholds for “normal” that lie somewhere between 35% and 45%. Although the concept of the ejection fraction is intuitively attractive, the focus on contractility is mechanistically flawed in its simplicity. Haemodynamics are more complex than measurement of contractility and the impairment of left ventricular filling may be as important as impairment of