Aim of our study is to examine some aspects of the relationship between pharmacokinetics and pharmacodynamics of Propafenon that are important as far as its current use is concerned. Orally administered Propafenon is largely absorbed and easily metabolized by the liver. Bioavailability is on the average 50%. Ninety per cent of the administered dose is eliminated in the feces and in the urine in about 60 hours. Because of the lack of a good correlation between chronically administered doses and plasmatic concentration, we tried to see whether the peak concentration after administration of a single dose could predict in some way the response of the patients arrhythmia. So far we do not have a clear cut answer to this question, which probably requires a different, more complex approach to the relations between pharmacokinetics, plasmatic levels and therapeutic range of an antiarrhythmic drug.