There is no single diagnostic test for HF because it is largely a clinical diagnosis based on a careful history and physical examination. The clinical syndrome of HF may result from disorders of the pericardium, myocardium, endocardium, heart valves, or great vessels, or from certain metabolic abnormalities, but most patients with HF have symptoms due to impaired left ventricular (LV) myocardial function. It should be empha- sized that HF is not synonymous with either cardiomyopathy or LV dysfunction; these latter terms describe possible structural or functional reasons for the development of HF. HF may be associated with a wide spectrum of LV functional abnormalities, which may range from patients with normal LV size and preserved EF to those with severe dilatation and/ or markedly reduced EF. In most patients, abnormalities of systolic and diastolic dysfunction coexist, irrespective of EF. EF is considered important in classi cation of patients with HF because of differing patient demographics, comorbid conditions, prognosis, and response to therapies (36) and because most clinical trials selected patients based on EF. EF values are dependent on the imaging technique used, method of analysis, and operator. As other techniques may indicate abnormalities in systolic function among patients with a preserved EF, it is preferable to use the terms preserved or reduced EF over preserved or reduced systolic function. For the remainder of this guideline, we will consistently refer to HF with preserved EF and HF with reduced EF as HFpEF and HFrEF, respectively (Table 3). 3. HF Classi cations Both the ACCF/AHA stages of HF (37) and the New York Heart Association (NYHA) functional classi cation (37,38) provide useful and complementary information about the presence and severity of HF. 