c-Cbl-associated protein (CAP), also called Sorbs1 or ponsin, has been described as an essential adapter protein in the insulin-signalling pathway. Here, we describe for the first time a unique protective role for CAP in viral myocarditis. Mortality and heart failure development were increased in CAP−/− mice compared to CAP+/+ littermates after Coxsackievirus (CVB3) infection. Mechanistically, CAP protected from tissue apoptosis because of reduced CD8+ T and natural killer cell cytotoxicity. Despite reduced cytotoxic elimination of CVB3-infected cells in CAP+/+ hearts, however, CAP enhanced interferon regulatory factor 3(IRF3)-dependent antiviral type I interferon production and decreased viral proliferation in vitro by binding to the cytoplasmic RIG-I-like receptor melanoma differentiation-associated protein 5 (MDA5). Taken together, these findings reveal a novel modulatory role for CAP in the heart as a key protein stabilizing antiviral type I interferon production, while protecting from excessive cytotoxic responses. Our study will help to define future strategies to develop treatments to limit detrimental responses during viral heart inflammation.