Coronary sinus pacer lead simulating left atrial mass.

M-mode and two-dimensional echocardiographic evaluation of a patient with rheumatic heart disease and an atrioventricular sequential pacemaker with a coronary sinus lead showed an echo-producing mass in the left atrium. A repeat study after the coronary sinus lead was replaced by a right atrial screw-in lead revealed the disappearance of the echo-producing mass.