Yes you can indeed scare someone to death especially if they already have heart trouble because if you scare the person good enough then it can cause the person to actually have a heart attack which is what kills them.
So you should never try to scare an elderly person because you would not know if they have a heart condition and the older people get the less healthy they usually are.
I've heard of some family members such as a grandson scaring their Grandpa who was in his 80s and he had a heart attack and died.
The Grandson felt so bad about it and blamed himself for killing his Grandpa and he did in a way but he was not trying to kill him.
If the person is really healthy then you're unlikely to kill the person or scare them to death where they actually die.