Thrombosis is an infrequent complication in mechanical valve prostheses carrying a vital risk for the patient. The performance of transesophageal echocardiography (TEE) is high in differentiating the thrombosis from other causes of flow obstruction and is fundamental for establishing treatment. Fibrinolysis is an effective alternative treatment to surgery when the latter carries a high risk. In the case herein reported TEE provided a rapid and precise diagnosis and allowed to prove the resolution of the prosthetic thrombosis following fibrinolytic treatment.