**Core Concept**
Kussmaul's sign is a clinical finding associated with increased jugular venous pressure (JVP) during inspiration, which is indicative of right heart failure or constrictive pericarditis. The mechanism involves the impaired ability of the right ventricle to accommodate increased venous return during inspiration.

**Why the Correct Answer is Right**
Kussmaul's sign is a result of the interplay between the increased negative intrathoracic pressure during inspiration and the inability of the right ventricle to adapt, leading to an increase in JVP. This is often seen in conditions where the right ventricle is stiff or constricted, such as constrictive pericarditis. In normal individuals, the right ventricle can accommodate the increased venous return during inspiration, but in cases of right heart failure or constrictive pericarditis, this accommodation is impaired.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Kussmaul's sign can be seen in right heart failure, which is characterized by impaired right ventricular function.
**Option B:** This option is incorrect because constrictive pericarditis is a condition where the pericardium is stiff and non-compliant, which can lead to Kussmaul's sign.
**Option C:** This option is incorrect because cardiac tamponade is a condition where the pericardial space is filled with fluid, which can also lead to Kussmaul's sign.

**Clinical Pearl / High-Yield Fact**
Kussmaul's sign is often remembered as "paradoxical rise" in JVP during inspiration, which is a key distinguishing feature from other conditions.

**Correct Answer: C. Cardiac tamponade.**