Designing bug-free medical device software is difficult, especially in complex implantable devices used for rhythm management of the cardiac or the neurological system. There is currently no formal methodology or open experimental platform to validate the correct operation of implantable medical device software. We describe our recent work on heart modeling for the validation and verification of artificial cardiac pacemakers. As we extend this platform to more complex devices such as cardioverter-defibrillators, there are several significant challenges in the modeling of biological systems and their patient-specific response to external stimulus. Our goal over the longer term is to explore the methodologies for experimental evaluation, modeling for validation and verification of implantable devices within the context of the underlying biological system. We present our early and promising results for simplified models and propose steps toward an integrated platform for validation of medical device systems.