It is time to look at heart failure with preserved ejection fraction from the right side.

H eart failure (HF) with preserved left ventricular (LV) ejection fraction (EF; or HFpEF) is seen in approximately half of patients with HF and confers morbidity and mortality similar to that of HF with reduced left ventricular ejection fraction (HFrEF). 1 HFpEF has been characterized by abnormal LV dia-stolic function, abnormal LV-central vascular coupling, impaired systolic reserve and chronotropic response during exercise, abnormal skeletal muscle function, and dysfunction of the right ventricle (RV)–pulmonary vascular (PV) unit. The pathophysio-logical heterogeneity underlying HFpEF likely explains, in part, why there are no HFpEF-specific therapies to date associated with improved survival in this population. Careful delineation of HFpEF subphenotypes on the basis of predominant patho-physiologic inputs may improve diagnostic classification, guide targeted therapy, and ultimately improve clinical outcome. Historically, the RV has been considered to play a minor role in maintaining adequate blood flow, and as a result, the importance of RV function in various cardiopulmonary diseases has been underinvestigated and often overlooked. 2 In the normal heart, the RV is closely coupled to a low-impedance pulmonary vascular system that is best considered as a RV-PV unit. 3 In the setting of increased RV afterload, it is increasingly recognized that RV function is critical for augmentation of forward cardiac output and prevention of systemic venous congestion. Accordingly, RV dysfunction (RVD) has emerged as a potent predictor of poor prognosis in pulmonary arterial hypertension, intrinsic lung disease, and HFrEF. In HFrEF, integrated indexes of RV-PV dysfunction such as the combination of RVEF <0.35 and elevated pulmonary artery pressure confer a 7-fold increase in mortality. 6 These findings have appropriately prompted efforts to therapeutically target the RV-PV unit with pulmonary vasodilators, with mixed results to date in HFrEF, 7,8 likely owing to whether patients selected had a high burden of RV-PV dysfunction. At present, the prevalence and prognostic significance of abnormal RV-PV structure and function in patients with HFpEF is not well established (Table). The study by Mohammed and colleagues 17 in this issue of Circulation represents an important step forward in our understanding of the burden and significance of RV-PV dysfunction in HFpEF as defined by multiple easily derived echocardiographic measurements. Strengths of the study include the investigation of a HFpEF cohort at a center of excellence in HFpEF and echocardiography with complete follow-up data available on HF hospitalization rate, cardiovas-cular mortality, and all-cause mortality; the establishment of an independent relationship between RVD and prognosis …