Relatively little is known about the psychophysiological processes underlying the development of socioemotional vulnerabilities that are common among adolescents exposed to child maltreatment. Using a prospective, longitudinal design, we investigated whether trajectories of resting heart period (HP; a physiological correlate of stress vulnerability) across three visits (separated by 6 months) was associated with shyness (a type of socioemotional vulnerability) in adolescent females exposed to child maltreatment ( N = 55; Mage = 14.07 years). Adolescents’ resting HP across visits was best characterized by two latent trajectories: a stable high class (25.5%) and a stable low class (74.5%). The stable low HP trajectory was associated with higher shyness at Time 1 (T1), and HP trajectory moderated the association between T1 and Time 3 (T3) shyness. Females in the stable low HP trajectory demonstrated stability of shyness from T1 to T3, whereas T1 and T3 shyness were unrelated for females in the stable high HP trajectory. We also found that shyness at T1 and T3 was associated with greater levels of anxiety at T3. These findings illustrate heterogeneity in the developmental patterns of resting autonomic activity in adolescent females exposed to child maltreatment; such differences may influence the continuity of some traits linked with socioemotional vulnerability such as shyness.