- I have heard recomendations from doctors on TV.
I can imply or emphasize that I have heard the recomendations at different times, at different places, not just once before. It can indicate someone's experience.
- I heard recomendations from doctors on TV.
It is more likely to refer to a situation that happened once before. So it implies that I heard recomendations (plural), not just singular one, at a time on the spot.
I know it depends on situation, but personally I think it is more natural situation that a person have heard reconmendations several time in his/her life. So, generally I would say #1. Am I right to think this way?