We have developed a computer simulation to evaluate the success of Implantable Cardioverter Defibrillators (ICDs) in a patient specific manner. Though we have verified the simulations by means of surface recordings of shock potentials in humans, recordings of potentials within the heart and torso are needed to further verify the model for use in a clinical setting. We suspended an ex-planted porcine heart in a torso shaped electrolytic tank and recorded potentials on the tank surface, the epicardial surface, and within the myocardium during ICD shocks and compared these recordings to finite element solutions based on the same geometries. Potentials recorded from the surface and within the volume of the torso tank agreed well with the simulated potentials. Quantitative comparison between recorded and simulated potentials showed a mean correlation of 0.90, a mean normalized RMS error of 0.102, and a mean relative error of 26.5%. These results suggest that our simulation model can guide the optimization of ICD design and use.