Atrial septal defects (ASD) are the most common congenital cardiac lesion in adults, representing up to 40% of acyanotic shunt lesions in patients older than 40 years. Secundum ASD comprises defects in the area of the oval fossa, and may be associated with other types of interatrial communications. We present a case of a 25 year-old female patient who was asymptomatic until the age 22 when she started presenting exertion dyspnea and lower limbs edema, during her third pregnancy. The patient was admitted in the emergency department because of a febrile respiratory distress syndrome dying in less than 36 hours after her arrival. The autopsy examination revealed pneumonia and a secundum ASD, associated with a rare form of interatrial communication, the inferior sinus venosus defect, which is characterized by an anomalous connection of the right pulmonary veins to the inferior caval vein at its opening in the right atrial cavity, while retaining partially their connection to the left atrium. A dysplastic and thickened mitral valve was also present. Signs of pulmonary hypertension confirm the Eisenmenger syndrome in this adult patient.