Early life adverse experiences can have long-term physiological and behavioral effects and enhance stress sensitivity. This study examined the effects of repeated maternal separation (MS) on cardiac autonomic stress responsivity and heart structure in adulthood. Male Wistar rats were separated from the dams for 3 h per day from postnatal day 2 through 15. When exposed to a 5-day intermittent restraint stress (IRS) as adults, MS and control rats showed similar modifications of cardiac sympathovagal balance, quantified via heart rate variability (HRV) analysis. In addition, MS had no effect on cardiac pacemaker intrinsic activity (as revealed by autonomic blockade with scopolamine and atenolol) and did not affect the circadian rhythmicity of heart rate, neither before nor after the IRS period. However, MS differed from control rats in cardiac parasympathetic drive following IRS, that was heightened in the latter but remained unchanged in the former, both during the light and dark phases of the daily rhythm. The evaluation of adult cardiac structure indicated that stress experienced during a crucial developmental period brought about modest changes, involving cardiomyocite hypertrophy, increased density of vascular structures, and myocardial fibrosis. Whether functional and structural changes could have evolved to a more pathologic phenotype later in life remains to be determined.