A 73-year-old woman presented with chest discomfort and New York Heart Association class 2 dyspnea when she climbed stairs 2 weeks ago. She was not taking any medication except hypnotics, and her only cardiovascular risk factor was old age. Although she had had 3 natural childbirths, she had no history of surgery or blood transfusions. No specific findings were observed upon physical examination, electrocardiography (ECG), or chest x-ray imaging, and cardiac biomarkers were within the normal range, but the D-dimer, prothrombin time (PT), partial thromboplastin time (PTT), and activated PTT levels were prolonged. Transthoracic echocardiography showed a normal left ventricular ejection fraction and no regional wall motion abnormality. On the basis of the exercise-induced ECG changes in the treadmill exercise test, coronary angiography was planned to conduct decision-making for appropriate management and prognosis assessment (class I, level of evidence B). After 300 mg of aspirin and 180 mg of ticagrelor were administered, coronary angiography was performed via the right radial artery. A significant stenosis was noted in the left anterior descending coronary artery and right coronary artery; thus coronary stenting was performed successfully using DES stents (Fig. 1). Unexpectedly, D-dimer, PT, and PTT prolongation were maintained at 6 and 24 hours after coronary stenting, and hemoglobin (HgB) decreased from 11.3 to 9.5 g/dL. Although ecchymosis and oozing were present at the right radial artery puncture site, no evidence of bleeding was observed. Aspirin (100 mg daily) and ticagrelor (90 mg twice daily) were administered to prevent a stent thrombosis. The test values to identify the causes of prolonged coagulopathy fell within the normal range. Epistaxis and blood-tinged sputum occurred on day 3 after coronary stenting. Because HgB had dropped to 8.5 g/dL, chest and abdominal computed tomography scans were performed to confirm the possibility of internal bleeding; however, no abnormal findings were observed except aortic calcification. The antiplatelet therapy measured using the Multiplate Analyzer (Roche Diagnostics, Mannheim, Germany) was adequate, but the daily dose of the antithrombotic agent was reduced to 100 mg of aspirin and 90 mg of ticagrelor. After transfusing 2 units of packed red cells, HgB remained >10 g/dL (Fig. 2). On day 5, factor V activity was 14% (reference range 60%–120%), but other laboratory findings, including factor VIII activity, were all within normal ranges; she was diagnosed with F5D based on low factor V activity. Hematochezia occurred on day 6, and ischemic colitis was confirmed via sigmoidoscopy (Fig. 3). After fasting, except antithrombotic agents and intravenous antibiotic treatment, a general diet was made available starting on day 8, and HgB was maintained consistently above 10 g/dL. However, PT, PTT, and D-dimer prolongation persisted. The area under the curve (AUC) was 20 (reference range 1–41) for ticagrelor and 18 (reference range 1–29) for aspirin with the daily maintenance dose of 90 mg of ticagrelor and 100 mg of aspirin, with which she was discharged on day 10.