AAS and anabolics have shown that they thin the blood and "prevent" clotting from happening. Since MSten is simply a legal AAS, then you have to imagine that it indeed thins the blood. This is why before a surgery even if you are an HRT recipient they want you off anything like AAS or blood thinners, etc..because it can prevent blood from clotting.
Smoking and alcohol consumption have been shown to increase blood clotting, so you should be avoiding both of those.
You also have to look at the increases in blood pressure that will happen with such compounds. Msten is going to cause a much higher increase in BP then the halo will. But both risk that. A valve controls blood flow and rhythm, etc..increases or decreases in BP can certainly effect it's performance. You DO NOT want this.
For that reason alone, I'd say you need to be safe then sorry and "if" you are going to do it, you should start with the Halo...actually the 4-andro might be even a safer bet for you then even the halo, though both are supposedly milder and less abusive then many other PH's.
With a valve in place, although my medical background was in the Neurological unit in the hospital and not Cardiac, I would personally steer clear of ANY oral PH or AAS. If you need a boost, i think you would be far safer looking into HRT or even something mild like D-aspartic acid, etc..for a mild testosterone boost.
I am running Msten solo myself right now. It reminds me of a dry slightly weak dbol.. Excellent product, but no way in hell I'd be taking an oral if I had a valve in my chest.