An arteriovenous fistula (AVF) is an abnormal connection between an artery and a vein, whereby the interconnecting capillary network is missing. Such a malformation frequently occurs in the deep midline regions of the brain, and the subsequent increased flow into the draining vein of Galen substantially dilates in an aneurysmal manner. Congenital forms of the aneurysmal dilatation of the vein of Galen (AVG) often lead to death in the neonatal period, predominantly due to cardiac failure caused by the increased venous inflow as a consequence of the intracerebral arteriovenous shunting. In the presented case a male baby suffered from a rare combination of a cerebral AVF and an atrial septal defect (ASD). He was born at week 38 of pregnancy and subsequently developed tachydyspnoe. Ultrasound (US) and CT scans revealed a large bilateral AVF with dilated basal venous sinuses, hydrocephalus and brain atrophy. In the heart, severe right ventricular hypertrophy, patent ductus arteriosus and an ASD were detectable by US. Neurosurgical consultation rejected the possibility of an operative treatment due to size and localization of the lesion and the existing irreversible brain damage. The child died because of cardiac failure 6 days after birth. Autopsy examination in the brain demonstrated a large conglomerate of dilated blood vessels predominantly in the midline and left occipital lobe, edema and hydrocephalus. In the heart, the ASD detected by US proved to be an ostium secundum-type lesion. Histologically, the conglomerate of vessels revealed features of an AVF and matched the characteristics of AVG. Consequences of chronic ischemic brain injury were also present, with ferruginated neurons suggesting intrauterine damage caused by a congenital AVF. Based on data in the literature, we assume that the left-to-right shunt due to increased venous influx into the heart caused not only cardiomegaly, but may have also interfered with the normal development of the atrial septum leading to an ASD, contributing to the rapid progression of the cardiac failure.