The spleen and ascitic fluid are rarely imaged by transoesophageal echocardiography. In this case perisplenic ascitic fluid was misdiagnosed as a left pleural effusion and led to unnecessary surgical opening of the left pleural space during aortic valve replacement. On review of the images, three features were found that differentiated perisplenic ascitic fluid from a left pleural effusion. First, the spleen has a uniformly homogeneous, echogenic appearance (unlike atelectatic lung). Second, perisplenic ascitic fluid can be seen to communicate with a lateral space (unlike pleural fluid). Third, perisplenic ascitic fluid lies entirely lateral to the descending aorta (unlike pleural fluid).