## Core Concept
The core concept being tested here involves the management of heparin overdose, which can lead to excessive bleeding. Heparin is an anticoagulant that works by enhancing the activity of antithrombin III, leading to the inactivation of thrombin and factor Xa. In cases of heparin overdose, it's crucial to rapidly reverse its anticoagulant effects to control bleeding.

## Why the Correct Answer is Right
The correct answer, **Protamine sulfate**, is a specific antidote for heparin. It works by binding to heparin and forming a stable complex that neutralizes heparin's anticoagulant activity. This allows the coagulation cascade to return to normal, effectively controlling excessive bleeding caused by heparin overdose. Protamine sulfate is administered intravenously and its effect is immediate.

## Why Each Wrong Option is Incorrect
- **Option A: Vitamin K**: This is incorrect because Vitamin K is used to reverse the effects of warfarin, a different type of anticoagulant that works by inhibiting the synthesis of vitamin K-dependent clotting factors. It does not counteract heparin's effects.
- **Option B: Fresh Frozen Plasma (FFP)**: While FFP can provide clotting factors to help manage bleeding, it is not specific for reversing heparin's effects and is generally used when there is a need for volume expansion or specific clotting factor replacement.
- **Option C: Tranexamic acid**: This is an antifibrinolytic agent used to prevent excessive bleeding in conditions like heavy menstrual bleeding or in surgical procedures. It does not reverse anticoagulation caused by heparin.

## Clinical Pearl / High-Yield Fact
A key point to remember is that protamine sulfate is the specific antidote for heparin overdose. However, it's worth noting that protamine can cause hypotension and anaphylactoid reactions, so it should be used cautiously and ideally in a monitored setting.

## Correct Answer: D. Protamine sulfate