Left triatrial heart is defined as division of the left atrium into two chambers, proximal and distal, by a variably perforated membrane. The data of appearance of symptoms, often in early childhood, is related to the degree of obstruction and the presence or not of an inter-atrial shunt. Widescale usage of echocardiography, the investigation of choice for this diagnosis, has led to the detection of this abnormality in older patients, sometimes asymptomatic, without pulmonary hypertension. Three adults were referred for transthoracic and transoesophageal echocardiography to investigate systemic embolic disease (2 cerebral, 1 mesenteric). Two other adults underwent the same investigations for diagnosis of the aetiology of atrial fibrillation with mitral regurgitation. Two cases were asymptomatic children, one with a clinically benign murmur and the other with ventricular extrasystoles with no malignant features. In these seven cases, transthoracic (n = 5) and/or transoesophageal (n = 7) echocardiography demonstrated a left atrial membrane corresponding to the classical description of cor triatrium. The Doppler study showed no obstruction in 6 cases and minimal obstruction in 1 case. In our series, as in similar cases reported in the literature, the diagnosis of a left atrial membrane did not lead to surgery. Although we do not know the long-term outcome of this abnormality in asymptomatic children, the observations of complications in the adult suggest a potential of evolution which poses the question of optimal management.