ADRB2 and Arrhythmia: Moreover, complete β-AR blockade (with propranolol) blunted the exercise-induced impedance differences between animals susceptible (S, n = 7) and resistant (R, n = 5) to ischemia-induced arrhythmias (during control test; S: −30 ± 2.4 vs. R: −17 ± 2.7 Ω, P < 0.05, but after β-AR blockade; S: −16 ± 1.5 vs. R: −10 ± 4.1Ω, N.S.).