Congenital diaphragmatic hernia (CDH) is in many respects a disorder of the circulation. Pulmonary hypertension due to abnormal pulmonary vasculogenesis and function results in increased afterload on the right ventricle (RV), and via mechanisms of ventricular interdependence in turn leads to biventricular cardiac failure. Recent work suggests that RV function in CDH may be a central determinant of illness severity, and not simply a secondary “side-effect” of pulmonary hypertension. New echocardiographic imaging modalities have revealed insights into cardiac performance in CDH, including the importance of early diastolic dysfunction. Diastolic dysfunction appears to be related to clinical course including early outcomes in CDH. Improved understanding of the role of cardiac function in CDH may allow better early prognostication and inform therapeutic decisions including timing of surgery. New treatment paradigms incorporating early assessment and targetted therapy to optimise cardiac function may allow us to improve outcome in CDH.