We report the case of a 24-year-old man who underwent surgical repair of a sinus venosus atrial septal defect. Transthoracic echocardiograms performed on Day 3 and 6 after surgery demonstrated a very early cardiac remodeling with dramatic reduction of the right ventricular and atrial dimensions paralleled by an increase in the size of the left ventricle. This case provides the first demonstration of a very early cardiac remodeling after repair of sinus venosus atrial septal defect.