A heart rate of 42 beats per minute, which is defined as 42 heart beats per minute in a quiet state, is considered bradycardia. Bradycardia can be physiologic or pathologic. Physiologic bradycardia is more common in athletes and long-term physical laborers, while pathologic bradycardia is more common in hypothyroidism, sick sinus node syndrome, and atrioventricular block. 1. Physiological bradycardia, the number of heartbeats per minute in a normal person in a quiet state is the heart rate, and the normal heart rate of adults is 60-100 beats per minute, and it is regarded as bradycardia when it is lower than 60 beats per minute. Physiological sinus bradycardia is often seen in athletes, long-term physical laborers, this group of people due to physical demand, cardiac output per beat increased, causing a corresponding decrease in heart rate. 2. Pathological bradycardia, mostly seen in hypothyroidism, patients with insufficient levels of thyroid hormones, cardiac activity is in a state of inhibition, the heart rate is lower than normal; pathological sinus node syndrome, sinus node lesions lead to atrial conduction delayed abnormality, the heart rate is lower than normal; atrioventricular block, from the atria to the ventricles of the electrical conduction slowed down or even disappeared, the heart rate is lower than normal. Bradycardia, with a heart rate of 42 beats per minute, requires early medical attention to identify the cause, and if it is pathologic, early intervention is needed to avoid serious consequences.