A 12-year-old, male Yorkshire terrier was presented for acute pulmonary oedema. Thoracic radiographs showed a linear metallic foreign body within the cardiac silhouette. Echocardiogram showed a hyperechoic line extending through the left ventricle, the mitral valve, leading into the left atrium. A 4 cm long Kirschner wire was surgically removed by left fourth thoracotomy. The dog died two days after surgery for acute pulmonary oedema. Necropsy showed thrombi on the mitral leaflets that impeded their movement.