Right pulmonary artery to left atrial fistula is a rare pathology characterised by a right to left shunt. Another important aspect of this pathology is the difficulty encountered in making a diagnosis, which is why the diagnosis is frequently delayed into adulthood. A description of two cases is used to emphasise the importance of the different modes of echocardiography as a diagnostic tool in diagnosis, as well as the two different clinical forms that it adopts: a group of patients suffering cardiac failure and cyanosis without apparent cause generally in neonates and a second group of mostly older patients with dyspnoea and cyanosis without apparent cause. Symptoms thus differ depending on the time of presentation and are related to the size of the fistula.