A 20-year-old woman required urgent replacement of a calcified prosthetic mitral porcine xenograft with a mechanical one during the 32nd week of pregnancy. Five weeks later the patient delivered a normal child. Following delivery the patient refused oral anticoagulant treatment and 7 months later she underwent emergency removal of a prosthetic valve thrombus. Six months later, still refusing anticoagulant treatment, she died of cerebral embolization. We suggest that the replacement of a degenerated biologic valve with another biologic valve should be considered in patients who refuse anticoagulant treatment and that patients with prosthetic xenografts should be kept under close medical follow-up, including echocardiography because of possible accelerated xenograft failure during and/or following pregnancy.