Accessory mitral valve tissue is an unusual congenital cardiac anomaly and a rare cause responsible for left ventricular outflow tract obstruction. An 18-year-old patient was referred to this hospital due to an occasionally noted heart murmur in a medical examination. Echocardiography facilitated the diagnosis of accessory mitral valve tissue. To relieve the left ventricular outflow tract obstruction, an operation including resection of the accessory mitral valve tissue, implantation of artificial chordae tendineae, and mitral valve annuloplasty was performed successfully. Postoperative echocardiography showed a complete relief of the mitral valve leaflets and a wide patent left ventricular outflow tract. However, transient ischemic attack and Horner's syndrome complicated the patient early postoperatively. He was administered with a high dose of aspirin, and he recovered shortly. Surgical removal is in so much mandatory as a definite diagnosis of accessory mitral valve tissue with left ventricular outflow tract obstruction is established. A prophylactic treatment should be applied to the patients with accessory mitral valve tissue in virtue of their susceptibility to neurological events.

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Conduit failure and explant is inevitable. This phenomenon is worse with a longer follow-up. Mechanisms involved in conduit failure are unknown, even though they were accounted for by calcification and extensive intimal proliferation, and somatic outgrowth. Homografts are commonly used and have experienced a long history. The pulmonary homograft is the most commonly used RVOT conduit, especially in small children, due to its excellent characteristics. The newly-developed Contegra conduit has become popular due to its availability in full sizes and the acceptable results obtained at intermediate follow-up. The Hancock conduit can function sufficiently well for as long as 5-10 years, and early valve failure is relatively rare. It is admissible to use the Hancock conduit as an interim measure for future conduit reoperation due to its adequate function until subsequent operation. The application of an autologeous tissue valved conduit should be considered when other alternatives are not available.