Over the last decade, remarkable progress has been made in the field of endovascular treatment of aneurysms. Technological advances continue to enable a growing number of patients with cerebral aneurysms to be treated with a variety of endovascular strategies, essentially using detachable platinum coils. Yet, coil embolization remains a very complex medical procedure for which careful planning must be combined with advanced technical skills in order to be successful. In this paper we propose a method for computing the complex blood flow patterns that take place within the aneurysm, and for simulating the interaction of coils with this flow. This interaction is twofold, first involving the impact of the flow on the coil during the initial stages of its deployment, and second concerning the decrease of blood velocity within the aneurysm, as a consequence of coil packing. We also propose an ap- proach to achieve real-time computation of coil-flow bilateral influence, necessary for interactive simulation. This in turns allows to dynamically plan coil embolization for two key steps of the procedure: choice and placement of the first coils, and assessment of the number of coils neces- sary to reduce aneurysmal blood velocity and wall pressure.