Hypoplastic left heart syndrome (HLHS) is a complex heart malformation that requires life-saving treatments. Parents experience numerous challenges as they learn to parent a child with complex care requirements. The following research question guided this qualitative study: Is the parenting process among parents of a child with HLHS characterized by exaggerated vigilant parental action, and if so, how does this influence parental response? Situated within a larger program of pediatric cardiology research, this study included data from two grounded theory studies with parents of children with HLHS. This secondary analysis involved a thematic content analysis using sensitizing concepts of uncertainty, protectiveness, support, and mastery of complex care. Transcribed data from 55 interviews with 24 mothers and 17 fathers of young children with HLHS were analyzed for relevant and recurring themes. In mastering skills required to care for their child with HLHS, parents contrasted what was in their hands with what was out of their hands. Vigilant parental actions were evident as parents became skilled at providing complex care. Parents said they were sometimes excessive in their vigilant actions. In retrospect they viewed this vigilance as appropriate in some situations but exaggerated in other situations. Understanding parents’ vigilant actions in response to their child's complex care can guide health care providers’ interactions with families. Long-term follow up, both clinically and through research, is needed to assess the long-term consequences of exaggerated vigilant parental action on the child, parent, and family, and to determine and evaluate appropriate and timely intervention.