This study assessed cardiac rate and rhythm by ambulatory monitoring in 23 patients with panic disorder or agoraphobia with panic attacks. The patients had a higher than normal mean daily density of ventricular premature complexes (VPCs), but complex ventricular arrhythmias were uncommon. Heart rate was greater during panic intervals than during asymptomatic periods. The prevalence of arrhythmias within symptomatic intervals was similar during panic, partial panic, and anxiety and was significantly higher than during asymptomatic intervals. However, most panic episodes had no arrhythmias, and arrhythmias during panic intervals were simple VPCs.