By comparison, rats with treatment of propranolol (10 mg/kg/day), a non-selective β-AR blocker had an arrhythmia score of 2.1 ± 0.3 (P < 0.05), and those treated with metoprolol (80 mg/kg/day), a selective β1-AR blocker had a score of 2.4 ± 0.2 (P < 0.05). The gene discussed is ADRB2; the disease is cardiac arrhythmia.