<s>[INST] context: Good ventricular function and low pulmonary vascular resistance are essential requirements for a successful Fontan procedure. The Fontan operation should not be performed when ventricular ejection fraction is less than 30% or ventricular end-diastolic pressure is greater than 15 mm. Hg. Pulmonary vascular resistance in excess of 4 Woods units should also be considered an absolute contraindication for Fontan correction. Age at the time of Fontan procedure does not appear to be a major risk factor, except before age 2 years. Although patients who have survived into the third or fouh decade are likely to have ventricular dysfunction, a Fontan procedure can be performed successfully in these older patients if ventricular function and pulmonary vascular resistance meet the above criteria. In patients with tricuspid atresia a competent mitral valve is impoant for satisfactory cardiac output after the Fontan procedure. The presence of severe mitral insufficiency, however, should not necessarily contraindicate the procedure. In these cases it is recommended that the mitral valve be repaired or replaced in combination with the creation of a bidirectional superior cavopulmonary anastomosis. A completion Fontan operation is performed later. Distoed or stenosed pulmonary aeries are common sequelae of systemic-to-pulmonary aery shunts and may result in unsatisfactorily high pulmonary vascular resistance. In most cases, these stenoses can be repaired at the time of Fontan correction or with a bidirectional superior cavopulmonary anastomosis. [/INST] question: Which of the following should contraindicate performance of the Fontan procedure? | options: A: Patient age of 25 years B: Severe mitral insufficiency C: Left ventricular end-diastolic pressure of 18 mm. Hg D: Right pulmonary aery stenosis | answer: C </s>