**Core Concept**
Amyloidosis of the heart refers to the deposition of amyloid fibrils in the myocardium, leading to restrictive cardiomyopathy. This condition is characterized by the accumulation of insoluble fibrils, derived from various precursor proteins, in the cardiac tissue, which disrupts normal cardiac structure and function.

**Why the Correct Answer is Right**
Amyloidosis of the heart typically presents with a characteristic electrocardiographic (ECG) pattern known as "low-voltage QRS complex." This is due to the infiltration of amyloid fibrils within the myocardium, which reduces the amplitude of the QRS complex on the ECG. The correct answer, **C) ↑ed mass/voltage**, is incorrect as amyloidosis is actually associated with low-voltage QRS complex, not increased mass or voltage.

**Why Each Wrong Option is Incorrect**
**Option A:** Arrhythmias can occur in amyloidosis, but they are not the most common or characteristic presentation. While arrhythmias may be present, they are not the hallmark feature of amyloidosis of the heart.
**Option B:** AV block can occur in amyloidosis due to the infiltration of amyloid fibrils in the conduction system, but it is not the most characteristic feature of cardiac amyloidosis.
**Option D:** Hypertrophic cardiomyopathy is a different condition characterized by thickening of the heart muscle, which can lead to outflow tract obstruction and other symptoms. It is not a characteristic feature of amyloidosis of the heart.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that cardiac amyloidosis often presents with a characteristic ECG pattern known as "low-voltage QRS complex." This is a crucial feature to recognize, as it can help differentiate cardiac amyloidosis from other conditions that may present with similar symptoms.

**Correct Answer:** C. ↑ed mass/voltage