The precursors of insufficient blood supply to the heart may be feeling weak, always wanting to sleep, feeling incompetent to do anything, or always irritable, panic attacks, rapid heartbeat, chest discomfort with the slightest activity, and possibly angina pectoris, which has never been present before. When angina appears, the pain is long and frequent, the effect of taking nitroglycerin is not obvious, sometimes there are gastrointestinal symptoms, such as nausea, vomiting, loss of appetite or sweating, bradycardia, severe arrhythmias, and great fluctuations in blood pressure, these are precursors of insufficient blood supply, you must go to the hospital in time to do an electrocardiogram or echocardiogram to see the function of the heart.