Hi, my son is a heroin user, my wife a I keep pleading with him to stop but what is the best way to approach it? He's been away to rehab for 28 days and IOP a few times however his arrogance is monumental and doesn't want to follow the procedures to kick the habit. My wife is a screamer and I try to reason with him, I know it's a hard thing to kick. Her screaming "gives " him a excuse to do it. Thank you for any advice.

Pleading doesn't work, nor does screaming. In fact both are counter-productive, so he's sort of right, although reasons are not excuses.
How old is he? He needs to be told he can't come back from rehab. Halfway house for a year.
Parents have to set rules and not give in. There has to be discipline and consistency, and repercussions. Talk to the rehab counselors or get some books out of the library.

An intervention. It is a little more harsh then what Joypulv was suggesting. The basic idea is that he needs to kick the habit and if he doesn't then there are some serious reprocussions. Most often it is that he's essentially kicked out of the family. None of you support his drug habit. By supporting him you indirectly support his drug habit. If he doesn't drop the habit then he gets no support. That might require him to be homeless or whatnot, but doing what you're doing is just enabling his habit and that's the worst thing you can do.

It isn't going to be easy, but he need to understand that his actions carry consequences.

Sounds like you have done your part in trying to get him straightened out. Make certain that you are satisfied that you have done all you can do. Don't look back in the future and blame yourself if something very bad happens to him, and it is likely it will if he goes on the street with his habits. Life on drugs is a short life. Maybe get your wife some anger management counseling. She may be the straw that breaks the camel's back.

He hasn't stopped because he hasn't hit rock bottom yet.

Do you provide a roof over his head?
Do you provide him with food? Money?

If the answer to any of these questions is "yes." You are enabling him. I see that he has been in rehab, but the bigger question is were you and your wife in counseling while he was in rehab? It is extremely important that not only the addict get help, but the family as well.

Your wife specifically needs some help in dealing with this. Being a "screamer" is no excuse. She needs to learn to table her temper as she is most likely pushing him toward the drug with her actions.

The two of you need not only to have an intervention, but consequences. He needs to find another place to live unless he is in recovery. Don't provide him money, don't allow him in your home unless he is in recovery, etc.