Cyber-Physical Systems (CPS) refer to the next generation of ICT systems that mainly integrate sensing, computing, and communication to monitor, control, and interact with a physical process to provide citizens and businesses with smart applications and services: healthcare, smart homes, smart cities, and so on. In recent years, healthcare has become one of the most important services due to the continuous increases in its costs. This has motivated extensive research on healthcare CPS, and some of that research has focused on describing the software architecture behind these systems. However, there is no secondary study to consolidate the research. This paper aims to identify and compare existing research on software architectures for healthcare CPS in order to determine successful solutions that could guide other architects and practitioners in their healthcare projects. We conducted a systematic literature review (SLR) and compared the selected studies based on a characterization schema. The research synthesis results in a knowledge base of software architectures for healthcare CPS, describing their stakeholders, functional and non-functional features, quality attributes architectural views and styles, components, and implementation technologies. This SLR also identifies research gaps, such as the lack of open common platforms, as well as directions for future research.