**Core Concept**
Hyperophic obstructive cardiomyopathy (HOCM) is a genetic disorder characterized by abnormal thickening of the heart muscle, leading to obstruction of blood flow. This thickening is most commonly seen in the septum between the ventricles, which can cause a dynamic left ventricular outflow tract obstruction.

**Why the Correct Answer is Right**
The characteristic feature of HOCM is a non-dilated left ventricle with a thickened septum, which can cause a left ventricular outflow tract obstruction. This obstruction can lead to symptoms such as chest pain, shortness of breath, and syncope. The thickened septum can also affect the mitral valve, causing mitral regurgitation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while a dilated left ventricle can be seen in other conditions such as dilated cardiomyopathy, it is not characteristic of HOCM.
**Option B:** This option is incorrect because while a thickened right ventricle can be seen in conditions such as pulmonary hypertension, it is not characteristic of HOCM.
**Option C:** This option is incorrect because while a non-thickened left ventricle can be seen in conditions such as hypertrophic cardiomyopathy with preserved ejection fraction, it is not characteristic of HOCM.

**Clinical Pearl / High-Yield Fact**
In HOCM, the thickened septum can cause a dynamic left ventricular outflow tract obstruction, which can be exacerbated by conditions such as exercise or stress. This can lead to symptoms such as chest pain and shortness of breath.

**Correct Answer:** C. Thickened left ventricular septum.