The case of a 68-year-old man with chest pain for 3 days is presented. Coronary angiography demonstrated subtotal occlusion of the mid-left anterior descending artery. A drug-eluting cobalt alloy stent was implanted after balloon dilation. On the 3rd postoperative day, echocardiography showed a ventricular septal rupture (VSR) (7 mm diameter) near the cardiac apex and ventricular aneurysm. On cardiac magnetic resonance imaging (MRI), the VSR was shown to be 11 mm in diameter. The membranous septum was 32 and 27.8 mm along the anteroposterior and superoinferior axes, respectively. The left-to-right shunt was apparent. Four weeks later, interventional therapy was performed to occlude the VSR according to the result of the MRI. The symptoms improved rapidly, and the patient was discharged. At the 4-month follow up visit, cardiac MRI revealed no shunt at the occlusion site, and the edge of the occluder was secured in the adjacent normal cardiac tissues. In conclusion, cardiac MRI could be considered for patients with a newly implanted cobalt alloy stent to provide an accurate assessment of VSR.