The pulse rate of 45 beats/minute is bradycardia, which is mainly considered to be caused by drug, cardiovascular disease and other diseases. 1. Drugs: Some drugs such as beta-blockers, lidocaine, amiodarone, reserpine, morphine, digitalis, quinidine, verapamil, neostigmine can cause sinus bradycardia and the symptom of a pulse rate of 45 beats/minute. 2. Cardiovascular diseases: acute myocardial infarction, myocarditis, endocarditis, pericarditis invading sinus node, chronic ischemic heart disease, inflammation of sinus node, thrombus, sinus node artery dilatation sinus node hemorrhage, familial sinus bradycardia, etc., can lead to bradycardia, the symptoms of the pulse rate of 45 beats per minute. 3. Other diseases: Some heart diseases, such as congenital heart disease, myocarditis or complications after heart surgery, damage to the heart tissue, ultimately leading to bradycardia. There are many other causes of 45 beats/minute pulse rate, including influenza, hypothyroidism, obstructive jaundice, etc. It is recommended to go to the hospital for further examination and diagnosis.