Infant cardiac activity: Developmental changes and relations with attachment

In this study the stability over the first 13 months of life of measures of infant cardiac activity (heart period and heart-period variability), their relations with each other, and their relations with a continuous-variable index of infant-mother attachment were investigated. The indexes of cardiac activity changed in an orderly way with development (increasing heart-rate variability, decreasing heart rate). There were moderate to high intercorrelations among the cardiac measures, particularly those indexing heart-rate variability (i. e., vagal tone, heart-period variance, and heart-period range)