Which substance is used to reverse the effects of heparin?

Protamine sulfate is the correct answer because it specifically counteracts the anticoagulant effects of heparin, which is a blood thinner commonly used to prevent and treat blood clots. Heparin works by inhibiting thrombin and factor Xa, leading to decreased clot formation. When there is a need to reverse the effects of heparin, such as in cases of excessive bleeding or prior to surgical procedures, protamine sulfate is administered.

Protamine sulfate functions by binding to heparin, forming a stable complex that neutralizes its anticoagulant effects. This allows for the restoration of normal blood coagulation. The use of protamine sulfate is well established in clinical settings, making it the go-to antidote for heparin.

In contrast, vitamin K is primarily used to reverse the effects of anticoagulants like warfarin and does not affect heparin. Calcium gluconate is used to address calcium deficiencies or certain types of overdose situations, and amiodarone is an antiarrhythmic medication used to manage certain types of heart rhythm disorders. These substances do not have a direct role in reversing the effects of heparin, which clarifies why they are not appropriate answers in this context.