Nosebleeds after cardiac bypass surgery are mainly considered to be caused by drug factors, but environmental factors, pathological factors such as nasal diseases, hematologic diseases, etc. cannot be ruled out. 1. Drug factors: cardiac bypass surgery itself does not cause nosebleeds, nosebleeds are mainly considered to be caused by postoperative anticoagulant drugs such as aspirin and other adverse reactions, such drugs can be antiplatelet aggregation, which may cause patients to have nosebleeds, blood in the stool, bleeding gums and other symptoms, serious need to be timely consultation under the guidance of the doctor to stop or adjust the dosage. 2. Environmental factors: such as dry air, nasal mucosa is relatively fragile and easy to bleed. 3.Pathological factors (1) Nasal diseases: such as nasal septum deviation, nasal inflammation, nasal cavity occupying lesions, etc. can cause nasal dryness, nasal mucosa dry local capillary rupture bleeding. (2) Blood system diseases: such as leukemia, thrombocytopenic purpura, aplastic anemia, etc. can cause nosebleed, but also other parts of the body bleeding, anemia, fever, sternal pain and other adverse symptoms. The causes of postoperative nosebleed after cardiac bypass surgery are not limited to the above factors, therefore, it is recommended to go to the hospital in time to find out the causes of nosebleed and then actively treat it, so as not to delay the condition.