Several healthcare processes are comprised of clinical actions that span over various independently managed healthcare organizations. Reserving resources for such healthcare processes implies the interoperation of independently managed healthcare organizations, which information systems are often based on proprietary solutions, and developed in piecemeal way. Reserving clinical resources in such an environment is problematic due to the autonomy and heterogeneity of the healthcare organizations information systems. Moreover, many healthcare processes have timing constraints, which complicate the reservation process. In particular, neither optimal resource allocation methods nor traditional transaction models can be deployed in a loosely coupled environment consisting of autonomous systems. In this paper, we present a new transaction model, called 2-phase reservation transaction, which can be used to ensure that clinical resources are reserved in an atomic way, and which minimize the efforts required for undoing the effects of the canceled clinical reservations. We also present how 2-phase reservation transactions can be implemented in Service Oriented Architecture by exploiting WS-Coordination. In addition, we present how Business Process Modeling Notation (BPMN) can be used in specifying the transactional requirements of the clinical resource reservation processes.