Theophylline increases the heart rate in patients with normal sinus rhythm and in patients with sick sinus syndrome. This effect is probably connected to the blockade of adenosine receptors by theophylline. This study evaluated the efficacy of theophylline in 34 elderly patients with symptomatic sinus bradycardia (age 68 +/- 11 years). A resting electrocardiogram, a 24-hour recording and treadmill test were performed both before and after administration of slow-release theophylline (700 mg/day). The drug increased resting heart rate (from 43 +/- 6 to 63 +/- 16 beats/min, p < 0.01), mean 24 hour heart rate (from 49 +/- 7 to 65 +/- 17 beats/min, p < 0.01), and minimal 24 hour heart rate (from 34 +/- 5 to 44 +/- 10 beats/min, p < 0.05 ). Cardiac pauses longer than 2.5 seconds were present in 8 patients during control recordings, and disappeared after theophylline. Twenty-six patients were followed for a period of 20 +/- 5 months. Suppression of symptoms was achieved in 24 of them. Asthenia and easy fatigue were reduced markedly by the drug. During long term therapy, the sinus rate was similar to that observed at the steady-state evaluation. In 6 of the 34 patients theophylline had to be discontinued because of gastric intolerance (in 4 cases at the end of the steady-state evaluation and in 2 during long-term therapy). These data suggest that oral theophylline can represent an effective therapy in some elderly patients with symptomatic sinus bradycardia and can avoid or delay the need of a permanent pacemaker.