It has recently become firmly established that patients can experience chronic and acute heart failure with a normal ejection fraction (HFNEF).1–5 We now know this disorder is the dominant form of HF in the community, and that compared with HF with reduced ejection fraction (HFREF), it is increasing in prevalence and incidence,6 causes at least as many hospitalizations and healthcare expenditures,1,6,7 causes at least as severe chronic symptoms and reduced objectively measured exercise tolerance,4 and, once patients are hospitalized, has death rates that are similarly grim.1,6 Until recently, however, we have invested nearly all our resources into understanding the pathophysiology and treatment of HFREF. As a result, a physician managing a patient with HFREF can rely on practice guidelines that are solidly supported by dozens of large trials demonstrating substantial improvements in each of the meaningful HF outcomes: mortality, hospitalizations, exercise intolerance, and reduced quality of life. When the patient instead has HFNEF, there is relatively little information about pathophysiology or treatment to guide the physician. This fact is reflected in outcomes, which a recent study indicates are improving in patients with HFREF but worsening in those with HFNEF.6 This disconcerting imbalance is magnified by sex and age, as the large burden of HFNEF falls primarily on older women.1,2,6 Article p 2051 In the present issue of Circulation , Westermann and colleagues8 report a welcomed and important study aimed at addressing the dearth of information about the pathophysiology of HFNEF. They studied 70 very well-characterized patients with documented symptoms of HF, normal left ventricular (LV) EF, and no other detectable cause for their symptoms, including pulmonary and ischemic heart disease. The investigators used a conductance catheter to measure pressure–volume loops during supine rest, handgrip exercise, and atrial pacing to 120 bpm. They …