BACKGROUND: Left ventricular diastolic dysfunction, with secondary atrial pressure elevation, is a well-known concept. On the contrary, effect of left atrial compliance on pulmonary pressure is rarely considered. CASE PRESENTATION: We report the echocardiographic case of a 9-year-old child who presented severe rheumatic mitral valve regurgitation with a giant left atrium, in contrast to a normal artery pulmonary pressure, testifying of the high left atrial compliance. CONCLUSION: Left atrial compliance is an important determinant of symptoms and pulmonary artery pressure in mitral valve disease.