One hundred forty-five consecutive patients referred for ambulatory electrocardiographic monitoring for the evaluation of palpitations were studied just before monitoring. They were compared with 75 asymptomatic, nonpatient volunteers. The research battery included a structured diagnostic interview, self-report questionnaires, and perceptual tasks measuring awareness of cardiac activity. After monitoring, symptom reports were compared with concurrent electrocardiographic recordings to determine their accuracy. Forty palpitation patients (27.6%) had DSM-III-R lifetime panic disorder, and 27 (18.6%) had current (1-month) panic disorder. Panic patients were significantly more likely to describe their palpitations as "racing" or "pounding" and to have been awakened from sleep by them. They did not have more cardiac arrhythmias during 24-hour, electrocardiographic monitoring, and their symptom reports were significantly less likely to be due to demonstrable cardiac irregularities. They were not more accurately aware of resting heartbeat than nonpanic palpitation patients. They did score higher on self-report measures of somatization, hypochondriasis, and bodily amplification.