Virtual Worlds (VWs) are computer simulated environments, in two-or three-dimensions (3D), where hundreds of people can interact with each other in real time. Current heuristic evaluation can potentially identify issues related to the usability of VWs, but it may miss domain specific problems. For this reason, the development and use of appropriate heuristics is highly significant. This paper describes the development and validation process of a novel set of usability heuristics for VWs applications and an associated checklist. An experimental evaluation showed that the new heuristic set can potentially identify usability problems that are more closely related to the VW context and that would not be found using the traditional Nielsen's heuristics.