Take it too hard is more American. They have similar meanings but as usual slight contextual differences. If you lost your job, your friend might say, "don't take it too hard, you'll find another job" - if your friend then didn't speak to you the next day, your mother might say, "don't take it to heart, I'm sure he likes you but maybe something happened in his life which has upset him". So it depends on the context but they have similar meanings, and now you've pointed it out (made me look at it) they sound very alike. "too hard - to heart" Nice one :)