I've actually done this and I won't say not to. It's just not realistic to expect someone to sit there when something... anything may work. I get it. Do prepare yourself for the storm afterwards though. I was and it wasn't that bad. Felt better to do something than nothing better to make a wrong decision than none at all. So I pressed.
But first determine what you think you will get out of contacting OW/OWH. This is the most important question and shouldn't be overlooked. If you just want revenge by contacting them you may get it. If you think it may be what's needed to stop the affair - it may. Just be sure to evaluate what you think will come out of it and whether it outweighs the pending storm. In my case it did, in yours it may not.
H 30 (me) W 28 Married 9 yrs 2 children EA found out on 7/5/07 ILYBNILWY 8/25/07 The unexamined life is not worth living -Socrates