We present a patient with severe decompensated esophageal achalasia in whom transthoracic echocardiography revealed compression of the left heart chambers caused by the dilated esophagus representing a posterior mediastinal mass. This case also illustrates the ability of echocardiography to monitor success of treatment of decompensated achalasia. An important role of echocardiography in the diagnosis of mediastinal masses is emphasized.