The impact of an atrial septal defect in the elderly with reduced diastolic elasticity of the left ventricle is unclear. We studied the hemodynamic changes during balloon occlusion of atrial septal defects in patients over 60 years of age. In 18 patients (61–78 years old; median, 70), the left atrial pressure and the mitral valve inflow was measured during complete balloon occlusion of the defect and after deflation of the balloon. In seven patients, the left atrial pressure and the E/A ratio of the mitral valve inflow increased markedly (P = 0.02). Mean atrial pressures reached values of 27 mm Hg and the v‐wave peak values of 55 mm Hg. Two patients received a transcatheter device closure and developed congestive heart failure. In the elderly, an atrial septal defect can have a decompressive impact on the left ventricle. Therefore, caution appears to be warranted if atrial septal closure is planned. Cathet Cardiovasc Intervent 2001;52:177–180. © 2001 Wiley‐Liss, Inc.