There will be tracheal intubation during cardiac surgery, which may cause some small damage to the mucous membrane and a small amount of blood in the postoperative sputum, which will usually disappear after a day or two. This kind of blood in sputum will be more clearly defined from the sputum, and the blood is mixed in only after the sputum is produced. There is also a case of blood in sputum, where the sputum is completely mixed with blood. This type of sputum can be found in patients with poor heart function. The sputum is mixed with red blood cells at the time of sputum production and appears as pink or bright red sputum; the patient may experience discomfort, difficulty in breathing or a rapid heart rate. If the bloody sputum does not tend to decrease, please give feedback to your doctor promptly. If you are unable to judge, please promptly ask the medical staff to help judge.