Why practice deep breathing and coughing before cardiac surgery: tracheal intubation and inhalation of anesthetic drugs during surgical anesthesia can cause irritation to the respiratory mucosa; the effect of extracorporeal circulation on the lungs during cardiac surgery and the large amount of rehydration make the postoperative airway secretions increase easily causing pneumonia and pulmonary atelectasis. Once pneumonia and pulmonary atelectasis occur, it will cause postoperative hypoxemia in patients, which may seriously cause myocardial ischemia and aggravate patients’ condition, which is not conducive to their postoperative recovery. Effective preoperative exercise of deep breathing and effective coughing and sputum excretion can help lung expansion and prevent postoperative pulmonary complications and hypoxemia.