Using electrocardiogram data with 78 six-month-old infants, this study examined the presence or absence of brief orienting bradycardia during the onset of maternal arm-restraint and subsequent differences between infants on behavioral organization during restraint. Results showed that 45 of the infants exhibited brief episodes of bradycardia at the onset of arm-restraint. Group comparisons showed infants exhibiting bradycardia to have greater emotional reactivity during the arm-restraint protocol, which included a shorter latency to cry, decreased orientation toward mother, increased escape attempts during restraint, greater intensity of crying, and longer duration of crying than non-bradycardiac infants. These findings suggest that bradycardia at the outset of a mild perturbation episode may signal infants' attention to the emotional content of novel dyadic interactions and the disruption of expectancies in ongoing interactions, leading them to become distressed more quickly, turn their attention away from mom, and attempt to escape the restraint with greater vigor. (Contains 2 tables and 1 figure.)