Cardio-vascular diseases are the prime cause of death in the Western World. Arteriosclerotic plaques may lead to an obstruction of the blood flow and can cause heart attacks and strokes. In this context, balloondilatation and stenting are established treatments to dilate the artery again and keep it open. Nowadays, the two traditional principles of science, theory and experiment, are complemented by numerical simulations as a third principle. Simulations of the process of balloondilatation may help to gain medical insight. In a current research project in Essen anatomical and physiological data of the arterial wall necessary for such simulations are obtained from the fusion of ultrasound imaging and X-ray angiographic data. The resulting finite element model is large and solved on a parallel computer using a sophisticated algorithm, the so called FETI domain decomposition method. The latter method has been used in the past by mathematicians and engineers to solve large systems of equations on supercomputers. This project is a common effort of mathematical, medical and engineering scientists and is supported by the Deutsche Forschungsgemeinschaft.