The objective of the submitted prospective study was to assess the influence of intravenously administered aminophylline on the sinoatrial node. The authors examined by electrophysiological methods 20 patients (16 without dysfunction of the sinoatrial node and 4 with dysfunction of the sinoatrial node). From the investigation patients were eliminated with an apparent and obvious cause of elevated uric acid serum levels and patients where on electrophysiological examination limited values of the corrected recovery time of the sinoatrial node were found (from 650 ms to 999 ms). To all 20 patients 240 mg aminophylline were administered by the i.v. route with in 2 mins. The following parameters were recorded: age, serum level of uric acid, basal heart rate in ms, corrected recovery time of the sinoatrial node in ms, heart rate and corrected recovery time of the sinoatrial node 5 min after completed administration of aminohpylline in ms. As regards age and uric acid serum levels there was no significant difference between dysfunction of the sinoatrial node and normal function of the sinoatrial node. Intravenously administered aminophylline hastened significantly the heart rate in patients without dysfunction of the sinoatrial node (p < 0.05). The value of the corrected recovery time of the sinoatrial node was shorter but the difference was not statistically significant. In patients with dysfunction of the sinoatrial node aminophylline did not affect the heart rate and corrected recovery time of the sinoatrial node.