This study examined how proximal and distal familial stressors influenced the real-time, dynamic individual and dyadic regulation of respiratory sinus arrhythmia (RSA) in mother-preschooler and father-preschooler interactions in at-risk families (N = 94, Mage = 3.03 years, 47% males, 77% White, 20% Latinx, data collected 2013-2017). Proximal stressors were operationalized as changing task demands (baseline, challenge, recovery) across a dyadic puzzle task. Distal stressors were measured as parent-reported stressful life events. Multilevel models revealed that greater proximal and distal stressors were related to weaker dynamic self-regulation of RSA in mothers, fathers, and children, and more discordant mother-child and father-child coregulation of RSA. Findings affirm that stress is transmitted across levels and persons to compromise real-time regulatory functioning in early, developmentally formative caregiver-child interactions.