Nate "grabs his blood," or "grabs his heart" before Hulk gets near him. Classic Nate tactic. Apparently Nate has better control of Hulk's body than Hulk does and his power can slip into Hulk effortlessly and control everything in his body from range instantly. And this isn't a Magneto likened example when he controls specific metals inside Hulk because that's his powers, this is just Nate grabbing pieces of Hulk and holding him there - because holding Hulk in place has always worked out - which begs the question of why Nate can't just control every fiber of his being?
Also Hulk has frozen solid before, and had cases where his blood was being frozen that he overpowered. Ant Man broke his hand punching Hulk's insides, Mr Fantastic was being crushed, and the classic 133 Hercs argument. So if his heart is grabbed that's connected to every other invunerable part, it seems likely he can overpower it.
Also Grey Gargoyle shenanigans and reverting Bruce being turned into glass, and multiple molecular devices.
We seem to want to build Nate into our own Sues and Magneto due to dislike of Hulk, but the difference that's even being conceded here - though why it's being discussed as an option in the first place is weird - is that those are actual attacks, while this is being argued as a time waster. Magneto can and will use the blood to attack Hulk. Not in long concentrated efforts to control Hulk, but to hurt him. And I don't even know if Sue can put a bubble in Hulk's brain, or if that would even work. Iirc Hulk was awake while they did brain surgery on him with a chainsaw.
But yes, Nate "controls" Hulks blood/heart because he can and will specifically target that off the hop no questions asked. But why just those things when there's nothing special within Hulk that specifically allows Nate control of those things? Is it because arguing that "Nate controls every molecule of Hulk" is a lot more ridiculous sounding and there's no way you could even toss that idea out there?
Anyway, that's provided he can simply bypass Hulk's outer exterior and disrupt his insides. He's no Magneto afterall.
"But what if he did not saying he will..."
No, you're just trying to put it out there as a possible weakness for Hulk for a character who doesn't need anymore.
"I'm not saying he will teleport his brain out of his body, but what if he did, wouldn't that be wild? Lol I wonder what Hulk would even do? Crazy thought! Nate is so exotic, look at all his powers while Hulk only has one way to win. CIS off Nate totally stomps lol, if only!"
Mega gay