Tidal Volume is a new podcast from ATS Peds focusing on core concepts of pediatric pulmonology. The goal is to bring in depth focus on these core concepts for residents, fellows, early career pulmonologists or even senior faculty looking for a refresher. In episode 3, Christopher Green MD and Christina Barreda MD from the University of Wisconsin discuss the concept of collateral ventilation. There is an overview of different models of ventilation and pathways of collateral ventilation, description of factors that influence collateral ventilation, followed by a discussion of the clinical relevance of collateral ventilation.