Electrophysiological effects of Ageratum conyzoides L. on the guinea-pig heart

An extract obtained from the leaves of Ageratum conyzoides L. changed the electrocardiogram, atrial impulse velocity, and coronary vessels resistance on isolated guinea-pig heart. Electrocardiographic alterations were: (a) PR interval increased from 80 +/- 1.4 ms to 105 +/- 14 ms (p < 0.01); (b) QT interval decreased from 170 +/- 2 ms to 154 +/- 7 ms (p < 0.01); (c) heart rate decreased from 170 +/- 17 bpm to 152 +/- 21 bpm (p < 0.01);(d) atrial impulse velocity decreased from 51 +/- 2 cm/s to 45 +/- 3 cm/s (p < 0.01);(e) the time spent for the impulse to be conducted from the atrium to the His bundle increased from 73 +/- 13 ms to 100 +/- 24 ms (p < 0.01). These effects disappeared after a washout.