Objective The demands of safety，reliability and system integrity for implantable medical devices are very high. As a class three medical device，we need to provide evidences that all engineer requirements are satisfied as part of system verification process. A design for testability methodology is presented for a microprocessor based on implantable pacemaker. Methods Because of the relationships between data and requirements are invariants，If we manage to collect similar data at different stages of firmware development，we may coordinate the unit and integration tests with system verification activities. We complete three experiments based on AAI mode as an example，analyze the test data and the relationships between data and requirements. Results The experimental results show that the method effectively completes the system functional verification and firmware test at different stages of firmware development. Conclusions This method can be used in systems with high safety and reliability requirement which are similar to cardiac pacemaker.