[Effect of ajmaline and its therapeutically used derivatives N-propylajmaline and di-monochloracetylajmaline on the functional refractory period and contractility of guinea pig atrium and aconitine arrhythmia in the rat].

1. In the isolated left atrium of the guinea pig ajmaline and di-monochloracetylajmaline (DCAA) show almost the same activity concerning prolongation of the functional refractory period. 2. In contrast to this N-propylajmaline (NPA) is much more effective than ajmaline. 3. NPA as compared to ajmaline and DCAA, however, shows a considerably smaller difference between the concentrations prolonging refractory period (I) and those decreasing contractility (II) in the guinea pig atrium (EC25). The quotient from I and II is 0.4 with NPA, 1.2 with ajmaline and 1.6 with DCAA. 4. Differences in efficacy similar to those observed in the guinea pig atrium are also found in experimental cardiac arrhythmias in the intact animal. NPA is much more effective than ajmaline regarding inhibition of extrasystoles, ventricular tachycardia and ventricular flutter due to aconitine infusion in the rat. In this experimental model DCAA shows slightly less activity than ajmaline; this difference is statistically significant.