To examine the alterations in adaptive responses to training by nonselective β-adrenergic blockade in patients with coronary artery disease (CAD), 26 patients were studied. Thirteen patients, aged 48 ± 2 years (mean ± standard error) were treated with β-adrenergic blocking agents and another 13, aged 55 ± 2 years, were control subjects. The 2 groups were similar in terms of initial maximal attainable O2 consumption V̇O2max): 24 ± 1 vs 25 ± 2 ml/kg/min, patients and control subjects, respectively), and intensity (87 ± 3.0 vs 88 ± 2% of attainable V̇O2max), frequency (4 ± 0.2 vs 4.0 ± 0.3 days/week), and duration (12 months) of training. Maximal attainable V̇O2 increased to the same extent (36% vs 35%) in both groups. Heart rate (HR) at rest decreased to a similar extent in both groups (p < 0.001). During submaximal exercise at the same exercise intensities, HR decreased in both groups, but to a larger extent in the control group than in the β-blocker group after training. In the latter, the reduced HR during submaximal exercise was solely due to training-induced bradycardia at rest. In contrast, the slower HR during submaximal exercise in control subjects after training was attributable to both bradycardia at rest and a smaller increase in HR during submaximal exercise. In both groups, the half-time of HR deceleration after cessation of exercise decreased (p < 0.005) after training. However, the training-induced decrease in the half-time was significantly larger (p < 0.025) in control subjects than in patients. The results suggest that β blockade does not attenuate the increase in maximal aerobic exercise capacity in response to training in patients with CAD. However, the adaptive responses to training during submaximal exercise and in the recovery period are altered by nonselective β-adrenergic blockade in these patients.