Objective: To evaluate the feasibility and accuracy of cardiac CT (CCT) in quantitation of extracellular volume (ECV) fraction in patients with heart failure, with 3 T Cardiac MR (CMR) as the reference. Methods: Twenty-eight patients with variety reasons of heart failure were enrolled in this study. ECVs was calculated, the correlation between CCT and CMR ECV value and other cardiac function parameters (left ventricular end systolic volume LVESV, left ventricular end diastolic volume LVEDV, cardiac output CO and ejection fraction LVEF, and clinical bio-marker BNP) was determined. Interclass correlation coefficient (ICC) was used to evaluate the agreement of measurement by two radiologists. Results: The average of ECV on CCT and CMR was 33%±8% and 31%±6%, respectively. A good correlation was revealed between myocardial ECV at CCT and that at CMR (r=0.854, P<0.001). Bland-Altman analysis between CCT and CMR showed a small bias (4.6%), with 95% limits of agreement of -18.2% to 27.4%. ICC for ECV at CCT was excellent (ICC=0.910). For both CCT and CMR, ECV was inversely related to LVEF. The radiation dose for CCT-ECV was (1.60±0.04) mSv. Conclusions: ECV at CCT and that at CMR showed good correlation, suggesting the potential for myocardial tissue characterization using CCT. However, CCT-ECV would possibly overestimate the extent of ECV. © 2019 by the Chinese Medical Association.