**Core Concept**
Ranolazine is an anti-anginal medication used to treat chronic angina. It works by inhibiting the late sodium current (I_Na) in cardiac muscle cells, which helps to reduce the intracellular sodium load and subsequently decreases the calcium overload that occurs during ischemia.

**Why the Correct Answer is Right**
Ranolazine's mechanism of action is unique among anti-anginal medications. By inhibiting the late sodium current, it reduces the influx of sodium ions into the cardiac muscle cells, which in turn reduces the subsequent influx of calcium ions through the sodium-calcium exchange mechanism. This decrease in calcium overload helps to reduce the frequency of angina episodes.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because ranolazine does not primarily work by increasing nitric oxide levels or relaxing vascular smooth muscle.
**Option B:** Incorrect because ranolazine is not a beta-blocker and does not primarily work by reducing heart rate or contractility.
**Option C:** Incorrect because ranolazine is not primarily a potassium channel opener and does not primarily work by increasing potassium ion efflux.

**Clinical Pearl / High-Yield Fact**
Ranolazine is particularly useful in patients with diabetes who have chronic angina, as it does not worsen glycemic control and can be used as an alternative to other anti-anginal medications.

**Correct Answer: B. Ranolazine does not primarily work by reducing heart rate or contractility.**