Betaxolol, a new .beta.-blocker, administered as a single dosage of 40 mg given orally, causes maximal heart rate reductions of 30% at rest, 28% during a submaximal exercise and 33% at rest after exercise. Heart rate reduction is still highly significant 48 h after administration at rest, during exercise as well as after exercise. During exercise, heart rate is still reduced by 23%, 48 h after administration. A smaller but still significant reduction in heart rate was found after the oral administration of 20 mg of betaxolol. Betaxolol appears more effective than a single oral dose of 160 mg of long-acting propranolol. No significant differences were found between 9 submaximal exercise tests performed within a period of 50 h in normal subjects.