French horn valves played with the left hand. Reason is that before brass instrument valves were invented a skilled player would use his hand in the bell to "bend" the notes in order to play a scale. As the majority of people or right handed the horn was played with the right hand in the bell. Once valves were added since players were already accustomed to having their right hands in the bell so the valves were fitted to be operated by the left hand. These days playing the notes is via the valves mostly, with the right handing "stopping" being more of a special effect. This is why the horn, unlike other brass instruments still has left handed valves. That said it's easy enough to swap to right handed play if having a go on another brass instrument, but is still one of those historical curiosities.
