A 78-year-old woman was operated on with a diagnosis of oozing-type cardiac rupture after an acute anteroseptal myocardial infarction. Pericardial drainage was performed and hemostasis was obtained by dressing with local hemostatics. As hemodynamics improved, elevation of pulmonary artery pressure and a step-up in oxygen concentration in the pulmonary artery from a Swan-Ganz catheter sample appeared. A left-to-right shunt was observed in the operative field with color Doppler echocardiography and a diagnosis of ventricular septal perforation (VSP) was made. Subsequently, intracavitary repair with two sheets of equine pericardial patch, sutured using interrupted mattress sutures with felt pledgets, was performed. Her early course after operation was satisfactory in spite of a small residual shunt. However, thirty-one days later she was returned to surgery because of an increasing residual shunt. Looseness of several interrupted mattress sutures and thrombus adherent to the internal surface of the pericardial patch were observed. The thrombus was removed and the patch was reattached using both interrupted mattress sutures with felt pledgets and continuous suture. She had an uneventful recovery thereafter. As double rupture is not a rare complication after myocardial infarction, a careful hemodynamic examination is necessary and important in the diagnosis and treatment of cardiac rupture. We consider that interrupted mattress sutures are a better technique for early repair of the VSP to reduce a risk of residual shunt due to the weakness and unclear border of infarcted myocardial tissue, and continuous suture is acceptable to repair the VSP 3 to 4 weeks later after infarction. Long-term anticoagulant therapy is necessary after intracavitary repair using equine pericardial patch.