Interaction of diltiazem with propranolol on atrioventricular conduction and refractoriness in the dog.

Propranolol pretreatment (0.1 mg X kg-1) significantly increased the lengthening induced by diltiazem (0.15 mg X kg-1 + 0.01 mg X kg-1 X min-1, 20 min) of the A-H interval of His bundle potential recordings in the dog. In the presence of propranolol, diltiazem also significantly increased the atrioventricular effective refractory period. The results suggest the possible occurrence of AV blocks as a result of the use of a diltiazem-beta blocker combination in clinical practice.