The NETDIAMOND Platform is a web-based system designed to record patient information in clinical studies, focused on a cohort of HFpEF patients. The system was designed to easily create a data schema based on groups of clinical data. For each group, the different institutions involved can read/edit the data of their patients. In the end, all data is combined as a unique dataset, with harmonised concepts and data structure. Additionally, there is an infrastructure to manage which entities can access each of these groups. This management is performed by a study manager using role-based access control policies at different levels. The system was developed for the NETDIAMOND project as a tool to support researchers by maintaining the patient clinical data, with the capability to export and analyse that data over time. This tool effortlessly enables patient follow-up by the responsible health professionals of each dataset, and the data sharing between different organisations. NETDIAMOND Platform is available online at: https://bioinformatics.ua.pt/netdiamond