Usually, stents cannot be placed in the hearts of those who have not reached the indication for stent implantation, those who have a short survival period for malignant diseases, those who have severe coronary artery blockage, those who have poor coagulation function, and those who are allergic to contrast agents. 1. If coronary artery stenosis <75% is indicated during coronary angiography and the indication for stenting has not been met, it is not suitable for stenting at this time. 2. If the patient has malignant tumor disease and has a short survival period, such as advanced lung cancer, liver cancer, gastric cancer, it is not meaningful to carry out stenting; at the same time, the body's immunity and repair ability is poor, so as to avoid other complications after the operation. 3. Coronary artery stenosis is so severe that the guide wire cannot pass through the stenosis; in this case, cardiac stent implantation is not possible and cardiac bypass grafting is needed to solve the problem from the outside of the coronary artery vessel. 4. If the coagulation function is poor, accompanied by the above gastrointestinal bleeding, and cannot take aspirin, clopidogrel and other anti-platelet aggregation drugs after the operation, it is usually not suitable for stent implantation. 5. People who are allergic to contrast media are also not suitable for stent implantation to avoid other complications such as contrast nephropathy, which is unfavorable to the postoperative recovery and may even threaten the safety of life. If stent implantation is needed due to medical conditions, it is recommended to go to the hospital in time and make a decision after the doctor's comprehensive evaluation of the condition.