Electrophysiologic investigation of the effects of antiarrhythmic drugs on sinoatrial conduction time (SACT) is conditioned by the inadequacies of indirect methods employing premature or asynchronous atrial stimulation. Direct recording of sinus node electrogram (SNE) is unaffected by the limitations of the indirect methods and is particularly useful when the effect of a drug on SACT is to be studied. In the present study the effect of propafenone on SACT directly (D) measured from SNE in 12 patients (7 male and 5 female subjects, 61 +/- 10 years) with normal sinus node function (NSNF) was investigated. DSACT, sinus node cycle length (SCL) and corrected sinus node recovery time (CSNRT) were evaluated before and 20 min after i.v. administration of 1 mg/kg propafenone. The following results (mean +/- SD) were obtained: in control condition SCL was 854 +/- 143 ms; CSNRT 316 +/- 82 ms; DSACT 88 +/- 20 ms. After propafenone SCL was 849 +/- 119 ms; CSNRT 340 +/- 93 ms; DSACT 97 +/- 15 ms (p less than 0.05). DSACT ranged from 60 to 105 ms and from 60 to 120 ms, respectively, before and after propafenone. In conclusion, in patients with NSNF propafenone 1. does not affect sinus node automatism and 2. prolongs significantly DSACT, which, however, remains within the upper normal limit.