Immunoglobulin G4-related systemic disease (IgG4-RSD) is a recognized emerging entity characterized by chronic fibroinflammation that can affect every organ but rarely affects the cardiovascular system. We report a rare case of IgG4-RSD involving an aortic valve that resulted in rapid progression of an aortic valvular stenosis and was successfully treated by aortic valve replacement and corticosteroids.