① The first heart sound is longer and the pitch is lower, while the second heart sound is shorter and the pitch is higher. ② The interval between the first heart sound and the second heart sound is short, while the interval between the second heart sound and the first heart sound is long, that is, the diastolic period is longer than the systolic period. ③ The first heart sound appears at the same time as apical beat and almost at the same time as carotid pulse. It is not appropriate to distinguish the first heart sound by the pulsation of radial artery, because it takes some time for the fluctuation of blood discharged from ventricle to reach the radial artery, so the pulsation of radial artery is later than the first heart sound. ④ The first heart sound is stronger at the apex of the heart and the second heart sound is stronger at the bottom of the heart. Generally speaking, it is not difficult to distinguish the first heart sound from the second heart sound, but in some pathological situations, such as increased heart rate and shortened diastolic period, the interval difference between heart sounds is not obvious, and the tones are difficult to distinguish, it is necessary to use apical pulse or carotid pulse to assist in the distinction.