Background.Heart failure with preserved ejection fraction (HFpEF) is associated with substantial morbidity and mortality. Existing data on cardiac structure and function in HFpEF suggest significant heterogeneity in this population. Methods and Results.Echocardiograms were obtained from 935 patients with HFpEF (left ventricular ejection fraction .45%) enrolled in the Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist (TOPCAT) trial before initiation of randomized therapy. Average age was 70- }10 years, 49% were women, 14% were of African descent, and comorbidities were highly prevalent. Centralized quantitative analysis in a blinded core laboratory demonstrated a mean left ventricular ejection fraction of 59.3-}7.9%, with prevalent concentric left ventricular remodeling (34%) and hypertrophy (43%), and left atrial enlargement (53%). Diastolic dysfunction was present in 66% of gradable participants and was significantly associated with greater left ventricular hypertrophy and a higher prevalence of left atrial enlargement. Doppler evidence of pulmonary hypertension was present in 36%. At least 1 measure of structural heart disease was present in 93% of patients. Conclusions.Patients enrolled in TOPCAT demonstrated heterogeneous patterns of ventricular remodeling, with high prevalence of structural heart disease, including left ventricular hypertrophy and left atrial enlargement, in addition to pulmonary hypertension, each of which has been associated with adverse outcomes in HFpEF. Diastolic function was normal in approximately one third of gradable participants, highlighting the heterogeneity of the cardiac phenotype in this syndrome. These findings deepen our understanding of the TOPCAT trial population and expand our knowledge of the diversity of the cardiac phenotype in HFpEF. © 2013 American Heart Association, Inc.