The heart rate and blood pressure response to exercise are clinically important parameters evaluated during treadmill testing. These responses may be altered by cardiac drugs. We evaluated the effect of procainamide and disopyramide on the heart rate and blood pressure response to treadmill exercise in 9 healthy volunteers. Each subject performed one Bruce protocol treadmill test while on each of three treatments: placebo, procainamide 1.0 g t.i.d.; disopyramide 150mg t.i.d. The order of the treatments was randomized in a Latin square design. The study was conducted double-blind. The drugs slightly increased the resting heart rate, but had no significant effect on exercising heart rate or blood pressure. We conclude that the use of procainamide or disopyramide does not interfere with the interpretation of results of treadmill testing.