There are no previous reports of rupture of a heterologous pericardial patch after aortic annulus enlargement. Our patient, a 72-year-old Japanese female, presented with congestive heart failure resulting from heart compression from pseudoaneurysm formation in the aortic root. At 57 years of age the patient had undergone replacement of the ascending aorta for Stanford type A acute aortic dissection. At 66 years of age she had undergone aortic valve replacement with a mechanical valve, accompanied by enlargement of the aortic annulus using an equine pericardial patch, for severe aortic valve stenosis with a narrow aortic annulus. Equine pericardial patch was used in the aortic annulus enlargement to form the aortic root from the ascending aortic vascular prosthesis to the non-coronary cusp of the aortic valve. We performed repeat median sternotomy under cardiopulmonary bypass with moderate hypothermia. The ascending aorta was balloon-occluded because of dense adhesions around the superior vena cava and ascending aorta due to the pseudoaneurysm. A tear in the equine pericardial patch was noted at the aortic root. The patient underwent pseudoaneurysm excision and repair of the aortic root using a double-layered, Hemashield-reinforced bovine pericardial patch. Routine follow-up with computed tomography should be performed for early detection of complications from a heterologous pericardial patch.