Prolonged sinus or atrial pause occurred in six patients with paroxysmal supraventricular tachycardia after drug administration. All six patients had normal sinus node function during control electrophysiologic study; the sinus cycle length ranged from 510 to 900 ms (mean 743 +/- 141) and the longest sinus node recovery time ranged from 800 to 1,230 ms (mean 1,018 +/- 168). A long sinus or atrial pause occurring at the termination of tachycardia or cessation of atrial pacing, ranging from 3,100 to 8,200 ms (mean 6,270 +/- 1,674), was provoked by the administration of various drugs. These included an intravenous bolus injection of adenosine triphosphate (5 mg; one patient), intravenous bolus injection of verapamil (5 mg; one patient), a combination of a single oral dose of diltiazem (120 mg) and propranolol (20 to 40 mg; three patients), oral diltiazem (240 mg/day; one patient) and a combination of oral diltiazem (240 mg/day) and propranolol (160 mg/day; one patient). In five patients, low frequency deflections suggestive of sinus node activity with a cycle length between 620 and 3,500 ms were recorded during pauses. These findings suggest that repetitive sinoatrial exit block was responsible for the pause. Sinus slowing with a long arrest suggesting suppression of sinus automaticity was also noted in three of these five patients; the longest sinus arrest in these three patients was 4,160, 4,800 and greater than 4,910 ms, respectively. The remaining patient with a pause of 6,840 ms had no recordable sinus activity, either reflecting suppression of sinus automaticity or technical failure.(ABSTRACT TRUNCATED AT 250 WORDS)