This article contributes to Science and Technology Studies on vulnerability by putting cyborgs at center stage. What vulnerabilities emerge when technologies move under the skin? I argue that cyborgs face new forms of vulnerability because they have to live with a continuous, inextricable intertwinement of technologies and their bodies. Inspired by recent feminist studies on the lived intimate relationships between bodies and technologies, I suggest that sensory experiences, material practices, and cartographies of power are important heuristic tools to understand the vulnerabilities of hybrid bodies. Based on an analysis of how patients in the Netherlands and the United States cope with appropriate and inappropriate implantable cardioverter defibrillator shocks, I describe how defibrillators introduce two new kinds of vulnerabilities: vulnerability as an internal rather than an external threat, and as harm you may try to anticipate but can never escape. Despite these vulnerabilities, some heart patients don’t position themselves as passive victims of faulty machines. They actively engage in material practices of resilience by using magnets to stop inappropriate shocks. I conclude that anticipating and taming the improper working of technologies inside bodies constitutes a new form of invisible labor that is crucial to diminishing the existential uncertainties of cyborgs.