**Core Concept**
The duration of a ventricular myocyte action potential is primarily determined by the balance between inward and outward ion currents during the plateau phase. The plateau phase is characterized by a slow inward calcium current (I_ca,L) and a slow outward potassium current (I_k1), which interact to prolong the action potential duration.

**Why the Correct Answer is Right**
The correct answer is due to the unique physiology of ventricular myocytes, which have a high density of L-type calcium channels. During the plateau phase, these channels allow a slow influx of calcium ions, which is balanced by the outward flow of potassium ions through the I_k1 channels. This interplay between inward and outward currents prolongs the action potential duration, allowing for a more efficient contraction of the ventricle. The slow inward calcium current (I_ca,L) is mediated by the L-type calcium channels, which are activated by the depolarization of the cell membrane and are regulated by the calcium-calmodulin complex.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately reflect the duration of a ventricular myocyte action potential. The action potential duration in ventricular myocytes is typically longer than 200-300 ms.
* **Option B:** This option is incorrect because it does not account for the unique physiology of ventricular myocytes. The plateau phase of the action potential is a critical component of ventricular myocyte physiology, and it is not simply a result of a slow depolarization.
* **Option D:** This option is incorrect because it does not accurately reflect the duration of a ventricular myocyte action potential. The action potential duration in ventricular myocytes is typically longer than 100-150 ms.

**Clinical Pearl / High-Yield Fact**
The duration of the action potential in ventricular myocytes is an important determinant of cardiac contractility. Alterations in the duration of the action potential can lead to changes in cardiac function, including arrhythmias and decreased contractility.

**Correct Answer:** C.