Blockchains are one of the most promising technologies in the domain of the Internet of Things (IoT). At the same time, healthcare monitoring is one of IoT applications where many devices are connected, and collect data that need to be stored in a highly secure way. In this context, we focus on IoT Blockchain architectures for healthcare monitoring applications. We start our study by exploring both IoT and blockchain technologies and identify how Fabric Hyperledger is a blockchain framework that fits our application needs. In this paper, we propose a security architecture based on this framework. We validate our approach first at a design level through concrete examples, then by showing some implemented functionalities.