The drug obviously has a positive use. My mother took it for years for a prolapsed mitral valve. I don't believe it's for high blood pressure but to regulate heart rhythm.
It has a number of uses, but it is definitely a first-line anti-hypertensive; I was originally on it for my blood pressure.
This is from the BNF (British doctors' prescribing bible). It mentions Arrhythmia, too.
PROPRANOLOL HYDROCHLORIDE
Additional information: interactions (Propranolol).
Indications: see under Dose
Cautions: avoid abrupt withdrawal especially in angina; first-degree AV block; portal hypertension (risk of deterioration in liver function); diabetes; history of obstructive airways disease (introduce cautiously and monitor lung function?see also Bronchospasm below); myasthenia gravis; history of hypersensitivity?may increase sensitivity to allergens and result in more serious hypersensitivity response, also may reduce response to adrenaline (epinephrine) (see also section 3.4.3); see also notes above; reduce dose of oral propranolol in hepatic impairment; renal impairment (Appendix 3); pregnancy (Appendix 4); breast-feeding (Appendix 5); interactions: Appendix 1 (beta-blockers), important: verapamil interaction, see also VERAPAMIL section 2.6.2
Contra-indications: asthma (important: see Bronchospasm below), uncontrolled heart failure, Prinzmetal's angina, marked bradycardia, hypotension, sick sinus syndrome, second- or third- degree AV block, cardiogenic shock, metabolic acidosis, severe peripheral arterial disease; phaeochromocytoma (apart from specific use with alpha-blockers, see also notes above)
BRONCHOSPASM. The CSM has advised that beta-blockers, including those considered to be cardioselective, should not be given to patients with a history of asthma or bronchospasm. However, in rare situations where there is no alternative a cardioselective beta-blocker is given to these patients with extreme caution and under specialist supervision
Side-effects: bradycardia, heart failure, hypotension, conduction disorders, bronchospasm, peripheral vasoconstriction (including exacerbation of intermittent claudication and Raynaud's phenomenon), gastro-intestinal disturbances, fatigue, sleep disturbances; rare reports of rashes and dry eyes (reversible on withdrawal), sexual dysfunction, and exacerbation of psoriasis; see also notes above; overdosage: see Emergency Treatment of Poisoning
Dose: by mouth, hypertension, initially 80 mg twice daily, increased at weekly intervals as required; maintenance 160?320 mg daily
Portal hypertension, initially 40 mg twice daily, increased to 80 mg twice daily according to heart-rate; max. 160 mg twice daily
Phaeochromocytoma (only with an alpha-blocker), 60 mg daily for 3 days before surgery or 30 mg daily in patients unsuitable for surgery
Angina, initially 40 mg 2?3 times daily; maintenance 120?240 mg daily
Arrhythmias, hypertrophic obstructive cardiomyopathy, anxiety tachycardia, and thyrotoxicosis (adjunct), 10?40 mg 3?4 times daily
Anxiety with symptoms such as palpitations, sweating, tremor, 40 mg once daily, increased to 40 mg 3 times daily if necessary
Prophylaxis after myocardial infarction, 40 mg 4 times daily for 2?3 days, then 80 mg twice daily, beginning 5 to 21 days after infarction
Migraine prophylaxis and essential tremor, initially 40 mg 2?3 times daily; maintenance 80?160 mg daily
By intravenous injection, arrhythmias and thyrotoxic crisis, 1 mg over 1 minute; if necessary repeat at 2-minute intervals; max. 10 mg (5 mg in anaesthesia)
