Myocarditis is an important cardiovascular disease, which can cause serious, and sometimes fatal, complications including heart failure, cardiac arrest, and dilated cardiomyopathy. It is commonly caused by infection and, most frequently, by viruses such as coxsackievirus B3 (CVB3). Viral myocarditis is difficult to treat, although interferon-β has shown promise. Recently, our laboratory showed that type I interferon (T1IFN) signaling into cardiomyocytes inhibits CVB3 replication, and minimizes viral myocarditis; inactivation of this signaling pathway led to acceleration and exacerbation of disease. However, the genes involved in these T1IFN-dependent events remained unknown. Using PCR array analysis of infected heart samples from cardiomyocyte-specific T1IFN receptor knockout mice, we identified IFIT family genes as ISGs that are highly expressed in cardiomyocytes during CVB3 infection. Subsequent validation assays by real-time PCR analysis revealed that cardiomyocytes express Ifit1, Ifit2, Ifit3, and Ifit3b in response to CVB3 infection. CRISPR/Cas9-mediated deletion of the entire IFIT family locus in a cardiomyocyte cell line, HL-1 cells, revealed the importance of these genes in T1IFN-mediated inhibition of CVB3 replication in vitro; after T1IFN stimulation, cells that lacked the IFIT gene family produced up to 26,362-fold more virus titer (P=0.0007) than did their genetically-intact counterparts. Notably, IFIT family knockout (IFIT KO) mice infected with CVB3 survived longer than CVB3-infected control C57BL/6 mice, and displayed few overt signs of disease, while control mice showed severe morbidity. Despite appearing generally healthy, post-sacrifice analyses of IFIT KO mice revealed profound myocarditis, accompanied by high titer of CVB3, whereas control mice showed limited histological changes and no detectable virus in heart. Finally, we found that – in contrast to the IFIT locus-deleted HL-1 cells – HL-1 cells that had been CRISPR/Cas9-edited to delete individual IFIT family genes remained relatively resistant to CVB3 replication, indicating that IFIT family proteins act coordinately to inhibit CVB3 replication and myocarditis.