the very first chord in the piece is very famous. it has become known as the "tristan chord". although it had been used before, the way wagner used it here was quite new. it makes the chromatic harmony very hazy, and the listener does not know for many bars what key the music is in. it creates a lot of tension. there are many other moments like this in the opera. the tension goes right through the opera. the story tells of a tension that can only come to rest through death.