In this paper we examine health literacy as a set of practices that unfold in networked activity systems. Focusing on the literacy practices of pregnant couples and parents of children with heart defect, we show that they participate in multiple activities with the object of constructing knowledge about the child's condition. The contexts for these activities are doctor-patient consultations and the parents' online searching and sharing. The study builds on ethnographic interviews, recorded medical consultations and collection of texts from online forums, blogs and social media. An analysis based on literacy practices and activity theory shows that these activities enable parents' learning, but they can also be restricting as to the mediating tools they provide and the rules that dictate the tools. Additionally, the object of learning about heart defect is not always clearly formulated and stable but it keeps alternating and expanding. As a result, the parents cross boundaries between activities with different mediating tools, rules and communities and thereby different possibilities for learning. We show that doing health literacy is comprised by a set of recontextualised practices of looking for medical and experiential knowledge and it is by a combination of the two that meaningful learning is achieved.