We monitored the electrocardiogram of 20 fathers while their child was born. Paternal heart rate rose on average by 53% during delivery from the starting point frequency (72 beats/min.) to the maximum (115 beats/min.) just before the birth of the child. Judging from the heart rate variation, paternal sympathetic activity increased by 25% and vagal tone decreased by 22% during delivery. No derangements in cardiac function were encountered, not even in the man who fainted.