They haven't gone into what exactly is wrong with his heart, yet. The parts with him in this issue bascially had the doctors all freaking out that they couldn't cut through his skin until Norman had Harrow come in with his power dampener. The issue ended with them just starting to operate on Cage while Bullseye whined about how Norman should just kill him and Norman saying, "Why would I kill him? There's so much more he has to offer us".