Background-Pulmonary vascular disease associated with left-side heart failure and preserved ejection fraction (PH-HFpEF) is an increasingly common cause of pulmonary hypertension. The distinction between PH-HFpEF and pulmonary arterial hypertension (PAH) is important because therapies indicated for PAH can be detrimental in HFpEF. Old age, the presence of hypertension and coronary artery disease, the absence of right atrial enlargement, higher aortic systolic pressure, higher mean right atrial pressure, and higher cardiac output best differentiated PH-HFpEF from PAH (area under the receiver operating characteristics curve; curve 0.97). Compared with HFpEF patients without pulmonary hypertension, PH-HFpEF patients were often female and more symptomatic, more often had right ventricular hypertrophy and right atrial enlargement, and had higher right atrial pressure. Conclusions-These data should help better identify PH-HFpEF, an entity that has become increasingly recognized and difficult to treat. (Circ Heart Fail. 2011;4:257-265.)