**Core Concept**
Propranolol is a non-selective beta-blocker that reduces sympathetic tone by blocking beta-1 and beta-2 adrenergic receptors. It is primarily used to manage cardiovascular conditions, hypertension, and certain arrhythmias.

**Why the Correct Answer is Right**
Propranolol's beta-blocking action can worsen conduction in the atrioventricular (AV) node, exacerbating partial atrioventricular block (Mobitz I or Wenckebach block). This is because beta-blockers decrease the rate of spontaneous depolarization in the AV node, leading to a delay or block in conduction. In contrast, other beta-blockers like atenolol and bisoprolol have a more favorable effect on AV conduction due to their beta-1 selectivity.

**Why Each Wrong Option is Incorrect**
**Option A:** Propranolol is actually useful in managing stable angina by reducing myocardial oxygen demand through its negative inotropic and chronotropic effects.
**Option C:** Idiopathic hypertrophic subaortic cardiomyopathy (IHSS) is a condition characterized by an abnormal thickening of the heart muscle, leading to outflow tract obstruction. Propranolol can help alleviate symptoms by reducing contractility and heart rate.
**Option D:** Familial tremor, also known as essential tremor, is a condition characterized by involuntary tremors of the hands, head, or voice. Propranolol, a beta-blocker, is effective in reducing tremor severity, possibly due to its effect on beta-2 receptors in the brain.

**Clinical Pearl / High-Yield Fact**
When considering beta-blocker therapy, it's essential to weigh the benefits against potential risks, especially in patients with pre-existing conduction abnormalities. Always evaluate the patient's cardiac status and potential interactions with other medications before initiating beta-blocker therapy.

**✓ Correct Answer: B. Partial atrioventricular block**