RESUMO
In this study we describe the normal electrocardiogram of the Guinea pig (Cavia porcellus), including the correlation between cardiac frequency and the Q-T interval. We studied the acute changes induced by an intraperitoneal dose of beta-methyl digoxin (0.2 mg). The drug produced a significant decrease in cardiac frequency and a significant prolongation of the P-R interval. It did not change the QRS duration or its position on the frontal plane. The Q-T interval, corrected by cardiac frequency, showed a tendency to decrease with treatment, but this change did not reach significance. The drug caused characteristic changes in ventricular repolarization: the T wave changed its polarity and S-T segment shifted to negative potential (between 0.05 and 0.15 mV). The possible origin of these observation is discussed