[John casts an irritated glance down at Mycroft. Of course he'd want to sever his heart. The Holmes brothers are entirely predictable sometimes. Although, John's not sure why Mycroft would have wished for the damn thing in the first place if he didn't want it. Egged on by Sherlock? That's the most likely scenario.

But the second part...]

He said what? [John's hackles rise.] I never told Sherlock that. I never told him that. He... he deduced you'd had your Heart severed after we got into a row about Sherlock severing his. He wanted to question you about it. I told him to piss off. [And so he had. Apparently he hadn't related the 'piss off' message to Mycroft.]