An unusual type of displacement of interventricular septum, the inverse of that found normally, was found by echocardiography in 3 cases: 2 with pulmonary arterial hypertension and 1 with constrictive pericarditis. In two cases catheterisation showed the haemodynamic picture of mitral obstruction, and in 1 case the typical findings on auscultation of mitral stenosis were present. The echocardiogram and anatomical studies showed that the mitral valve was normal. The obstruction was due to displacement of the septum towards the left ventricle during diastole. Because of this displacement, the septum came into contact with the mitral valve, and caused impairment of the filling of the left ventricle.