Figure 4.

Frequency-dependent effects of dofetilide and propranolol on the effective refractory period in the right ventricular papillary muscles of rabbits (a) and guinea-pigs (b). After measuring baseline values, separate groups of preparations were treated with pro-pranolol (300 nM), dofetilide (100 nM), dofetilide+propranolol (Dof+Prop) or were used as control. Each incubation period lasted for 30 min. Values are means±s.e.m., n indicates the number of experiments. Data are expressed as percentage changes in comparison with the baseline values (*P<0.05, ***P<0.001 vs 3 Hz in the same group. °P<0.05 vs dofetilide at the same frequency).