Objective:To investigate the clinical characteristics and structural and functional cardiac changes in heart failure with preserved ejection fraction(HFpEF)complicated with atrial fibrillation(AF)in elderly patients.Methods:As a cross-sectional study, 835 patients with HFpEF aged ≥60 years admitted to the Department of Geriatric Cardiovascular Medicine of the First Hospital of Lanzhou University between April 2009 and December 2020 were divided into an HFpEF+ AF group(267 cases)and an HFpEF group(568 cases)according to whether they had AF in addition to HFpEF, and their cardiac structure and function were evaluated.The optimal cutoff point of the ratio of the peak early diastolic velocity(E)to the maximum early diastolic velocity(e')of the mitral annulus(E/e')was analysed using the receiver operating characteristic(ROC)curve.The HFpEF+ AF group was divided into two subgroups, E/e'>11 and E/e'≤11, and differences in their clinical presentation, cardiac structural and function, and the relationship between the left and right heart were compared.Results:Compared with the HFpEF group, the left atrial volume index(LAVi)was larger[(60.0±23.3)ml/m 2vs.(43.9±19.0)ml/m 2, t=10.130, P<0.01]and the left ventricular ejection fraction(EF), mitral annular septal systolic velocity(s' S)and E/e' were smaller than in the HFpEF+ AF group(all P<0.01), whereas the right ventricular diameter(RVD), right atrial diameter(RAD)and area(RAA), tricuspid regurgitation velocity(TRv), and pulmonary arterial systolic pressure(PASP)in the HFpEF+ AF group were all greater than those in the HFpEF group(all P<0.05).In the E/e'>11 subgroup of HFpEF+ AF, the prevalence of hypertension, coronary heart disease and diabetes were higher, AF courses were shorter, and the decline of s' was more severe(all P<0.05).Furthermore, E/e' was independently correlated with LAVi, as was LAVi with PASP( t=2.114, 1.963, P=0.034, 0.042).The above-mentioned features were similar to those in the HFpEF group.The E/e'≤11 subgroup had a higher proportion of women, longer duration of AF than the E/e'>11 subgroup(median: 5 years vs.1 year, P=0.003), more noticeable enlargement of the right ventricle and right atrium, higher TRv and PASP( P<0.05). Conclusions:In elderly patients with HFpEF complicated with AF, the left atrial volume is increased further, and left ventricular systolic function and right heart morphology show serious deterioration, suggesting there might be two phenotypes of HFpEF+ AF with different pathophysiological mechanisms.