Distributed algorithms are subtle and error-prone. Still, very few of them have been formally verified, most algorithm designers only giving rough and informal sketches of proofs. We believe that this unsatisfactory situation is due to a scalability problem of current formal methods and that a simpler model is needed to reason about distributed algorithms. We consider formal verification of algorithms expressed in the Heard-Of model recently introduced by Charron-Bost and Schiper. As a concrete case study, we report on the formal verification of a non-trivial Consensus algorithm using the proof assistant Isabelle/HOL.