A patient has received an overdose of intravenous heparin, and is showing signs of excessive bleeding. Which substance is the antidote for heparin overdose?

A. Potassium chloride is used for hypokalemia. B. Vitamin K is the antidote for warfarin, not heparin. C. Vitamin E is not an antidote and can actually increase bleeding risk. D. Protamine sulfate binds to heparin and neutralizes its anticoagulant effect.