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Purpose To evaluate the prognostic utility of cardiac MRI parameters, particularly native T1 and extracellular volume fraction (ECV), for predicting early mortality in a preclinical model of anthracycline-induced cardiotoxicity. Materials and Methods Thirty-one Sprague-Dawley rats received weekly intravenous doxorubicin injections (2 mg/kg) for up to 12 weeks and were followed up until natural death. Cardiac MRI, including parametric mapping sequences, was performed. Myocardial histology was evaluated after death. Cox proportional hazards regression with time-dependent covariates was used to assess the association between MRI variables and early death. Results Of the 31 rats, 17 (55%) died before 12 weeks (early death group), and 14 survived to study completion. In the early death group, native T1 and ECV increased between weeks 4 and 6 (from 1210.51 msec ± 53.75 to 1368.09 msec ± 60.11 and from 17.52% ± 2.05 to 21.63% ± 2.22, respectively; both P < .001). At week 6, both parameters were higher in the early death group than in the survival group (1368.09 msec ± 60.11 vs 1243.10 msec ± 55.71, P = .003; 21.63% ± 2.22 vs 18.47% ± 2.13, P = .045). In univariable analyses, native T1 (hazard ratio, 1.01; 95% CI: 1.00, 1.01; P < .001) and ECV (hazard ratio, 1.17; 95% CI: 1.04, 1.32; P = .01) were statistically significantly associated with early death. A model combining native T1 and ECV achieved a C-index of 0.76 (95% CI: 0.64, 0.92). Conclusion Native T1 and ECV were good predictors of early mortality in rats with anthracycline-induced cardiotoxicity. Keywords: Animal Studies, MR-Imaging, Cardiac, Myocardium, Experimental Investigations Supplemental material is available for this article. © RSNA, 2026.