The obvious answer is to ask your surgeon, and you should.
My hospital OHS guide said I could "resume sexual activities as soon as you feel ready to do so."
Like most other males, I took that to mean first chance I got. One caution: if you've had a sternotomy, you should not be on top. Not even a little.
If you don't have other health issues, and had standard valve replacement/repair, and your doctor hasn't specifically told you a reason why you must refrain from ***, there is no automatic "waiting period" required by the surgery itself. Whoever wrote the 4-6 weeks in that one hospital guide simply pulled the number from his or her butt - or maybe figured it was "logical" to tie it to the healing of the sternum. No science to it. Of course, it wouldn't hurt to go a little easy for a while.
Not everyone heals at the same pace, or is affected the same way by things, so some may not be ready for *** right out of the box. Most people in the US are put on beta blockers after valve surgery, so the beta blocker may affect things for some males. But if you are ready, and have no other issues going on, you should be fine for it. The only problem is that you could have trouble chasing your intended around the room, as you can't run as fast as normal, and may not be able to catch her.
What it all boils down to is that you'll know when you're ready. There's no magic waiting period. If you're interested enough to ask, you're probably ready.
Best wishes,