With a combination of fetal catheter interventions and postnatal catheter and surgical interventions, the left ventricle in patients with hypoplastic left heart can undergo significant increase in size and remodeling to support cardiac output. However, some will have persistent high left atrial pressures resulting in pulmonary edema and high pulmonary artery pressures, that is, diastolic dysfunction.The manuscript details the medical and surgical strategies to diagnose and treat diastolic dysfunction in this patient population to promote biventricular circulations.Often times, this diastolic dysfunction is related to the presence of endocardial fibroelastosis, which affects left ventricular filling and mitral valve function. Ongoing research is investigating what causes and promotes the development of endocardial fibroelastosis, and means to improve the medical and surgical treatment of diastolic dysfunction.