A patient who had suffered an anterior MI and had PTCA and stent to mid LAD was referred for a pre discharge echocardiogram. Echo showed wall motion abnormality in LAD territory with mild MR. A cor triatriatum sinister was an incidental finding with no obstruction to flow across the opening in the membrane in the LA. 3D echo demonstrated the membrane beautifully. Key point Unexpected findings on echo should not be ignored and 3D echo can help in making the diagnosis.