Virtual reality-based therapy simulation meets a growing interest from the medical community due to its potential impact for the training of medical residents and the planning of therapies. However, computer models of the human anatomy are often very computationally demanding, thus incompatible with the constraints of such interactivesimulations. In this paper, we propose a fast model of the cardiacelectrophysiology based on an eikonal formulation implemented with an anisotropic fast marching method. We demonstrate the use of this model in the context of a simulator of radio-frequencyablation of cardiac arrhythmia from patient-specific medical imaging data. Indeed, this therapy can be very effective for patients but still suffers from a rather low success rate. Being able to test different ablation strategies on a patient-specific model can have a great clinical impact. In our setting, thanks to a haptic 3D user interface, the user can interactively measure the local extracellular potential, pace locally the myocardium or simulate the burning of cardiac tissue as done in radio-frequencyablation interventions.