We have studied the effect of the intravenous administration of the following drugs on ventricular refractoriness in 35 experiments in open chested beagle dogs: atenolol 0.2 mg X kg-1; nadolol 0.05 mg X kg-1; oxprenolol 0.2 mg X kg-1; pindolol 0.04 mg X kg-1; propranolol 0.2 mg X kg-1; sotalol 0.6 mg X kg-1 and timolol 0.1 mg X kg-1. The animals were anaesthetised with chloralose and urethane. Measurements were made of left ventricular epicardial monophasic action potentials (MAP) (n = 35) and the left ventricular paced evoked response (PER) (n = 25) at a fixed paced cycle length of between 220 and 310 ms. The animals were initially beta-blocked with iv pindolol or propranolol and the drug under study then administered iv 10 min later. The results were as follows: (control and post drug administration) MAP: nadolol 151 +/- 12 SD to 172 +/- 13 SD (p less than 0.001); oxprenolol 153 +/- 21 to 178 +/- 20 (p less than 0.001); sotalol 153 +/- 19 to 176 +/- 20 (p less than 0.001); atenolol 152 +/- 25 to 153 +/- 23 (NS); pindolol 149 +/- 11 to 152 +/- 10 (NS); propranolol 152 +/- 26 to 155 +/- 26 (NS); timolol 144 +/- 23 to 144 +/- 21 (NS). PER: nadolol 172 +/- 14 to 190 +/- 20 (p less than 0.001); oxprenolol 164 +/- 16 to 188 +/- 15 (p less than 0.001); propranolol 166 +/- 22 to 173 +/- 18 (NS).(ABSTRACT TRUNCATED AT 250 WORDS)