Abstract Body: Anthracyclines are a key component in the management of pediatric cancers long recognized to carry significant risk of dose-dependent cardiotoxicity. Despite advances in clinical management, considerable variation in the incidence of cardiotoxicity persists across dosing regimens suggesting modifiers exist predisposing susceptible individuals to advanced remodeling. Previous studies on childhood cancer survivors who later developed cardiomyopathies identified a susceptibility genotype postulated to alter the splicing pattern of TNNT2, the gene encoding cardiac troponin T (cTnT), increasing expression of its fetal isoform. Thus, we propose that fetal-cTnT can act as a genetic modifier, physiologically expressed in early life, that can alter anthracycline induced cardiomyopathic progression. Using Time Resolved Fluorescence we identified four common anthracyclines (Mitoxantrone, Doxorubicin, Daunorubicin, and Epirubicin) that alter the lifetime decay of labeled cardiac thin filaments, suggestive of direct binding. Isothermal Titration Calorimetry confirmed that Mitoxantrone has a higher binding affinity for complexes containing fetal-cTnT. We assessed the functional impact of fetal-cTnT during anthracycline treatment using 2D echocardiography in mice treated with 3 mg/kg/week Doxorubicin to a cumulative dose of 21 mg/kg. While treated NT mice had a transient reduction in contractile function, fetal-cTnT mice showed prolonged loss of contractile function, diastolic dysfunction, and ventricular remodeling. Consistent with the clinical risk factors, female mice had accelerated impairments and delayed recovery after treatment cessation compared to male mice. To explore the molecular pathways associated with these functional changes we performed transcriptional analysis. We observed a 2- to 7-fold increase in interferon signaling, known to be associated with cardiotoxicity and altered cardiomyocyte metabolism, beyond that elicited by Doxorubicin in NT mice. These data suggest that expression of fetal-cTnT may increase binding of anthracyclines to the myofilament, eliciting accelerated cardiac dysfunction, representing a unique, targetable genetic risk factor for anthracycline cardiotoxicity.