Electrocardiographic correlates of ventricular activation sequence were studied in 22 Macaca mulatta monkeys, aged
1-18 years, and 145 human subjects, aged 11-72 years, using the corrected orthogonal lead system of McFee-Parungao and the dipolar electrocardiotopographic (DECARTO) data presentation, where the time series of instantaneous spatial vectors are converted into time series of areas of activation on a spherical image surface enveloping the heart. Macaques had shorter ventricular activation time (6111 vs. 9711 ms) that could not be explained exclusively by their higher heart rate. Their DECARTO image of the resultant activation front occurred 10 ms after QRS onset (septal activation) identically with humans, but it attained a more anteriorly oriented maximum earlier than in humans (20 vs. 40 ms). The time course of the extent of the resultant activation front in old macaques (15-18 years) resembled to that observed in humans. On the average, female macaques had smaller DECARTO images of activation fronts throughout the QRS complex than males. This finding is in agreement with the known smaller QRS amplitudes in women than in men.