Heparin-induced thrombocythopenia (HIT) is a potentially serious complication of heparin treatment, rarely observed in cardiological wards. We present a case of a 38-year-old woman with dilated cardiomyopathy and massive pulmonary embolism treated with alteplase and unfractionated heparin. On 12th day an unexpected fall in platelet count was observed, without new signs of thrombosis. The HIT type II was diagnosed. Patient was treated effectively and safely by 7.5 mg of fondaparinux given subcutaneously once daily for 10 days.