Idiopathic dilatation of the right atrium is an isolated enlargement of the right atrium in the absence of other cardiac lesions. This rare anomaly has a clinical spectrum ranging from asymptomatic to heart failure or even sudden death. It can be associated with atrial arrhythmias and thrombus formation. Antiplatelet therapy is prescribed in most cases reported in the literature, and reduction plasty is indicated when there is rapid growth of the right atrium, compression of adjacent structures, or refractory arrhythmias. We report four cases of idiopathic dilatation of the right atrium diagnosed during prenatal screening. We describe the intrauterine course and management in postnatal life until early childhood.