Heart failure with preserved ejection fraction (HFpEF) is the clinical syndrome of heart failure (HF) in the presence of a normal or near-normal left ventricular (LV) systolic function. Some studies suggest that HFpEF may now be the predominant HF phenotype. It is associated with considerable morbidity and mortality, and outcomes have not improved over recent decades. The diagnosis of HFpEF can be challenging, and there is inconsistency and debate regarding which diagnostic criteria should be used. Various pathophysiological mechanisms have been implicated in the development of HFpEF; however, there is unlikely to be a single unifying paradigm. Instead, it is a condition characterised by a complex interplay of various cardiovascular mechanisms and associated comorbidities, with marked phenotypic variation between patients. To date, randomised controlled trials (RCTs) have failed to demonstrate a prognostic benefit, but several large trials of promising therapies with hard clinical endpoints are due to report soon. Future RCTs are likely to focus on assessing targeted therapies in sub-phenotypes of HFpEF.