A patient with a Björk-Shiley mitral prosthesis developed progressive heart failure without heart murmur and hemolysis. The prosthetic dehiscence was not diagnosed using transthoracic echocardiography, but transesophageal echocardiography. The regurgitant signals revealed laminar flow pattern with large regurgitant orifice. In patients with mitral prosthetic dehiscence with laminar flow pattern, transesophageal echocardiography can provide reliable diagnostic information.