**Core Concept**
Ranolazine is a medication used to treat chronic angina, and it works by inhibiting the late sodium current (INa) in cardiac myocytes. This action helps to reduce sodium overload and subsequent calcium overload, leading to a decrease in intracellular calcium and a reduction in myocardial oxygen demand.

**Why the Correct Answer is Right**
Ranolazine primarily targets the late sodium current in cardiac myocytes, which is an important mechanism for its anti-anginal effects. This action is distinct from other anti-anginal medications that primarily work through vasodilation or reduction of heart rate. By inhibiting the late sodium current, ranolazine reduces the amount of sodium that enters the cardiac myocyte, leading to a decrease in intracellular calcium and a reduction in myocardial oxygen demand.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because ranolazine does not work primarily through vasodilation. While it may have some indirect effects on blood vessels, its primary mechanism of action is through the inhibition of the late sodium current.

**Option B:** This statement is incorrect because ranolazine does not have a significant effect on heart rate. Its primary mechanism of action is through the inhibition of the late sodium current, which does not directly affect heart rate.

**Option C:** This statement is incorrect because ranolazine does not have a significant effect on beta-adrenergic receptors. Its primary mechanism of action is through the inhibition of the late sodium current, which is distinct from the action of beta-blockers.

**Option D:** This statement is incorrect because ranolazine is not a potassium channel opener. Its primary mechanism of action is through the inhibition of the late sodium current, which is distinct from the action of potassium channel openers like pinacidil.

**Clinical Pearl / High-Yield Fact**
Ranolazine is unique among anti-anginal medications in its mechanism of action, and its primary effect is through the inhibition of the late sodium current in cardiac myocytes. This makes it an important option for patients with chronic angina who require an alternative to traditional anti-anginal medications.

**Correct Answer: D. Ranolazine is a potassium channel opener.**