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AIMS: Epicardial adipose tissue (EAT) is increasingly recognized as an important factor in the pathophysiology of heart failure (HF). Cardiac magnetic resonance (CMR) imaging is the gold-standard imaging modality to evaluate EAT size, but in contrast to echocardiography, CMR is costly and not widely available. We investigated EAT thickness on echocardiography in relation to EAT volume on CMR, and we assessed the agreement between observers for measuring echocardiographic EAT.METHODS AND RESULTS: Patients with HF and left ventricular ejection fraction >40% were enrolled. All patients underwent CMR imaging and transthoracic-echocardiography. EAT volume was quantified on CMR short-axis cine-stacks. Echocardiographic EAT thickness was measured on parasternal long-axis and short-axis views. Linear regression analyses were used to assess the association between EAT volume on CMR and EAT thickness on echocardiography. Intraclass correlation coefficient (ICC) was used to assess the interobserver agreement as well as the intraobserver agreement. EAT on CMR and echocardiography was evaluated in 117 patients (mean age 71 ± 10 years, 49% women and mean left ventricular ejection fraction 54 ± 7%). Mean EAT volume on CMR was 202 ± 64 mL and ranged from 80 to 373 mL. Mean EAT thickness on echocardiography was 3.8 ± 1.5 mm and ranged from 1.7 to 10.2 mm. EAT volume on CMR and EAT thickness on echocardiography were significantly correlated (junior-observer: r = 0.62, P < 0.001, senior-observer: r = 0.33, P < 0.001), and up to one-third of the variance in EAT volume was explained by EAT thickness (R2 = 0.38, P < 0.001). The interobserver agreement between junior and senior observers for measuring echocardiographic EAT was modest [ICC, 0.65 (95% confidence interval (CI) 0.47-0.77], whereas the intraobserver agreement was good (ICC 0.98, 95% CI 0.84-0.99).CONCLUSIONS: There was a modest correlation between EAT volume on CMR and EAT thickness on echocardiography. Limited agreement between junior and senior observers for measuring echocardiographic EAT was observed. EAT thickness on echocardiography is limited in estimating EAT volume.