Nowadays, security is one of the biggest concerns against the wide adoption of on-demand Cloud services. Specifically, one of the major challenges in many application domains is the certification of exchanged data. For these reasons, since the advent of bitcoin and smart contracts respectively in 2009 and 2015, healthcare has been one of the major sectors in which Blockchain has been studied. In this paper, by exploiting the intrinsic security feature of the Blockchain technology, we propose a Software as a Service (SaaS) that enables a hospital Cloud to establish a federation with other ones in order to arrange a virtual healthcare team including doctors coming from different federated hospitals that cooperate in order to carry out a healthcare workflow. Experiments conducted in a prototype implemented by means of the Ethereum platform show that the overhead introduced by Blockchain is acceptable considering the obvious gained advantages in terms of security.