Cardioplegia, or propranolol tablets, which is a non-selective beta-blocker. Its side effects are: first, central nervous system, can appear vertigo, or low blood pressure caused by dizziness, mental depression, slow reaction, especially for the elderly, can appear blurred. Secondly, the heart rate can be slow, and the heart rate per minute can be less than 54 beats per minute. Third, more rarely, there are tracheospasm and dyspnea, breathlessness and cardiac insufficiency. Fourth, more rarely, there is fever, sore throat, and bleeding due to thrombocytopenia, and there can be a rash due to an allergic reaction. Fifth, if the adverse reaction persists, one should be particularly alert to diarrhea, cold extremities, dry eyes or skin, nausea, numbness of the fingers or toes, and unusual fatigue. Changes in blood pressure as well as heart rate should be closely monitored, and if a slowing of the heart rate occurs, the medication should be stopped immediately.