A thorough understanding of cardiorespiratory interactions is essential when caring for critically ill children. These interactions are linked to changes in intrathoracic pressure and their impact on cardiac preload and afterload. The predominant effect of positive-pressure ventilation in children with normal cardiac function is to decrease preload to the right heart with an eventual decrease in left ventricular stroke volume. This can be anticipated and mitigated by judicious fluid resuscitation. The effect of positive-pressure ventilation on right heart afterload is more complex and variable depending on lung volume. In patients with diminished left ventricular contractility, positive pressure reduces afterload to the left heart, significantly improving stroke volume. Monitoring of cardiorespiratory interactions in critically ill children is beneficial in assessing volume status and predicting fluid responsiveness.