Today, left atrial dissection is described as a rare complication of cardiac surgery, particularly after a mitral valve replacement. We report a rare case of left subacute atrial dissection occurred as a result of a domestic accidental fall. Transesophageal echocardiogram, angio-computed tomography, and magnetic resonance imaging showed an intramural formation with clear margins and a seamless cleavage with the posterolateral wall of the left atrium, which determined an obstacle to the ventricular filling. The patient was then operated in order to empty the hematoma and reattach the atrial wall.