Early postnatal developmental changes of the cardiac electric field in guinea-pigs.

Changes of the "representative" maximum spatial cardiac vector were followed daily from the 1st till the 3th postnatal day of life in a group of 70 guinea-pigs. This vector representing the spatial vectorcardiographic loop shifted gradually during the observation period from the right caudal quadrant to the left caudal quadrant attaining its new spatial orientation on the 7th day. This shift is accompanied by a transitory tilt in the cranial direction with a peak on the 7th day and a transitory decrease of the spatial magnitude with a peak on the 4th day. There was no significant difference between the spatial magnitude of the "representative" maximum vector on the 1st and the last (13th) day of observation.