Atrioventricular block response to exercise and intraventricular conduction at rest.

Sixty patients with atrioventricular block were exercised and monitored by a radioelectrocardiograph. Cases with a bundle-branch block QRS pattern at rest presented an improvement of atrioventricular conduction on exercise in I2@5 per cent, no change in 43-8 per cent, and an impairment in 43 8 per cent of cases. Corresponding figures in cases with no intraventricular conduction defect were 6I 4 per cent, 24 O per cent, and I3 6 per cent (P<o-ooI). Heart rate, neural tone, and myocardial ischaemia in relation to the refractory period length and the localization of the lesion are considered as factors possibly accounting for the difference in response to exercise between the two groups.