The fight between Arad and the Great Titanoboa Wyrm had lasted long enough, and he was going to end it soon. Because, as powerful as the Titanoboa was, it wasn't a real dragon, and that meant more than one thing.
There are many aspects that set True Dragons apart from the other creatures with draconic blood, and one of them is their insides. A red dragon's internal temperature is so high that it could melt steel; that's why stabbing one usually results in the sword melting.
Green dragons' organs are coated in their poison, and like that, all dragons are internally immune, or close to immune, to their own element.
Unless Alcott came to mess up with them like he did with Claug.
Arad's own organs are stored inside his stomach, meaning that his torso is empty. Stabbing him in the heart won't do anything, because there are no heart or lungs in his chest. They are all protected by his void.
