Recently there has been a renewed interest in cyborgs, and particularly in new and emerging fusions of humans and technologies related to the development of human enhancement technologies. These studies reflect a trend to follow new and emerging technologies. In this article, I argue that it is important to study ‘older’ and more familiar cyborgs as well. Studying ‘the old’ is important because it enables us to recognize hybrids’ embodied experiences. This article addresses two of these older hybrids: pacemakers and implantable cardioverter defibrillators inserted in the bodies of people suffering from heart-rhythm disturbances. My concern with hybrid bodies is that internal devices seem to present a complex and neglected case if we wish to understand human agency. Their ‘users’ seem to be passive because they cannot exert any direct control over the working of their devices. Technologies inside bodies challenge a longstanding tradition of theorizing human–technology relations only in terms of technologies external to the body. Cyborg theory is problematic as well because most studies tend to conceptualize the cyborg merely as a discursive entity and silence the voices of people living as cyborgs. Inspired by feminist research that foregrounds the materiality of the lived and intimate relations between bodies and technologies, I argue that creating these intimate relations requires patients’ active involvement in sustaining their hybrid bodies. Based on observations of these monitoring practices in a Dutch hospital and interviews with patients and technicians, the article shows that heart cyborgs are far from passive. On the contrary, their unique experience in sensing the entangled agencies of technologies and their own heart plays a crucial role in sustaining their hybrid bodies.