There are issues of interoperability, privacy and security in the current Electronic Health records (EHR) system. To overcome these challenges the authors have proposed a patient-centric multichain Decentralized Health Data Management (DHDM) system. This system makes use of the multichain framework of the polygon to provide interoperability across the authorized hospitals and polygon with a multichain structure. It acts as a conduit for external systems information, while also enabling the deployment of health records on the Ethereum blockchain with smart contracts. With focus on fully decentralization of the current medical healthcare system, DHDM aims to address the scalability and cost issues that are sometimes connected with the blockchain based apps by storing records on the Interplanetary file system (IPFS). This work also emphasizes the current challenges of the EHR system, which includes security, privacy, and interoperability difficulties despite its widespread use. When data is shared among the various healthcare institutes, it not only affects the price but also the quality of the data. The authors have proposed a secure means of collecting, obtaining and uploading data by putting a decentralized DHDM on blockchain. This method would improve the way medical data is being managed, which would increase the healthcare system overall efficiency.