A case of thrombosis on an aortic bioprosthesis after the fourth month of implantation is presented. The patient had been well anticoagulated for the first three months after surgery. A suspicious diagnosis was made when the patient started with symptoms of cardiac failure and angina and an Echo-Doppler showed a significant transvalvular gradient. The definitive diagnosis will be determined with the removal of the valve at surgery. Although this is a rarity as an early complication, it should be kept in mind in such cases. Surgical intervention is mandatory and life-saving.