You posted in the wrong place, having an ICD ( implanted cardioverter/defibrillator) is not a disability, quite the opposite

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The ICD is there to rescue him from sudden death, the cause of death of the two children that died, the boy at Mission Space and the girl at one of the water parks. The girl had Cardiomyopathy and the boy had a ventricular muscle band, both conditions are very high risk for sudden death-ventricular fibrillation. If the children had ICDs they would not have died, but their conditions were not previously known.
Sorry, to the point. Your father has his own little paramedic with him at all times to rescue him from any arrhymias ( too fast or too slow heart beats).
Let him do what he feels up to and enjoy his life.
Stay away from any electrical and magnetic fields. Electrical fields, such as arc welding,can cause the ICD to think the heart is too fast. Magnetic fields will turn the ICD off only while the magnet is close to the ICD, which is why they told him to use a phone in the opposite ear. Once the magnet is removed the ICD will turn back on.
If one of the rides precipitates an arrhythmia the ICD will take care of it. Make sure he takes his medications,doesn't get dehydrated,doesn't over-do-it, and use common sense. A year since it was implanted everything is healed up well enough nothing will pull out if he goes on Space Mountain.
Run it by his Doctor, since he is more familiar with his particular condition.
Relax and enjoy your trip,that is why he got his ICD in the first place- to experience and enjoy more life.
Jim-Cardiac Cath Lab and Cardiac Electrophysiology RN