If this is part of his doctors records then by law he is already allowed to see it. The official records are part of the doctors practice and required to be maintained by the doctor, but the patient is legally required to be provided a copy.
Even the Navy has to provide a copy of their medical records to the service member upon request. yes he may have to pay for the cost of generating the copy, but he has a right to the information.
The problem is that he wants real-time access to raw data from the device. The manufacturer records data about his heart and proprietary data about how the device is functioning. Very interesting dilema from a software development standpoint. The manufacturer needs to develop a solution for patients, but that will increase production costs.