Treadmill exercise test performance and ambulatory heart rate and activity patterns of 40 patients with panic attacks were compared with 20 age-matched controls (control group 1) and 20 nonexercising controls (control group 2). All patients underwent a symptom-limited exercise stress test. Panic attack patients and control group 1 wore an ambulatory heart rate/activity monitor for up to 3 days. Panic patients had a significantly higher heart rate at 4 and 6 METS than either control group. The max METS were 11.2 +/- 2.3, 13.5 +/- 2.3 and 11.2 +/- 1.8 for the panic attack patients and control groups 1 and 2, respectively. One panic patient had ischemia on the treadmill at 12 METS. Panic patients had a significantly higher standing heart rate than controls. Furthermore, 11 of 39 panic patients had tachycardia on standing compared with 3 of 40 controls. Panic attack patients had higher wake and sleep heart rates than control group 1, but the differences were not significant. These results are consistent with autonomic dysfunction in panic patients but may also be due to differences in physical conditioning. The treadmill can be useful for reassuring patients and for identifying the rare patient with ischemia on exercise.