The first heart sound occurs at the beginning of the cardiac systole and is low in pitch and long in duration (about 0.15 seconds). The causes include the contraction of the ventricular muscle, the sudden closure of the atrioventricular valve and the subsequent ejection of blood into the aorta, among other vibrations. The best place to hear the first heart sound is at the fifth intercostal space in the midclavicular line or at the right border of the sternum. The best place to hear the first heart sound is at the fifth intercostal space in the midclavicular line or at the right sternal border. It is also known as Holter monitoring. Dynamic electrocardiogram (DCG) can record all the abnormal waves and detect all kinds of arrhythmias and asymptomatic myocardial ischemia in various states within 24h, providing an accurate and reliable basis for the diagnosis of various heart diseases. In clinical application, it has a high detection rate especially for early coronary artery disease. Dynamic ECG can continuously record and analyze the changes of ECG in active and quiet states for a long time, which has diagnostic significance for heart diseases. 2.Doppler echocardiography There are many red blood cells in the blood, which can reflect and scatter ultrasound and can be considered as a tiny source of sound. The probe is placed in the rib cage without moving and emits ultrasound. When red blood cells flow in the heart or large blood vessels, the sound frequency scattered by the red blood cells changes. As the red blood cells move toward the probe, the reflected sound frequency increases, and vice versa, decreases. This difference in sound frequency between the red blood cells and the probe in relative motion is called the Doppler shift. It shows the speed and direction of blood flow and the nature of the blood flow. Doppler echocardiography is divided into pulsed Doppler echocardiography, continuous wave Doppler echocardiography, and color Doppler echocardiography. The most commonly used is pulsed Doppler echocardiography, which can trace the real-time Doppler spectrum of blood flow at any point in the heart under two-dimensional image monitoring and positioning. Cardiovascular angiography is the rapid injection of contrast agent into the heart or blood vessels through the cardiac catheter, so that the heart and blood vessel cavities are visualized under X-ray irradiation, and the process of visualization of the heart and blood vessel cavities is filmed by rapid film, television photography or magnetic tape recording. It is a valuable method to diagnose the heart and blood vessels. It is a valuable method to diagnose cardiovascular diseases. Doppler echocardiography can be used to analyze the thickness of the heart wall, the speed, amplitude, slope and trajectory of high-speed motion of valves, the direction of blood flow and the nature of blood flow. 5.Electrocardiogram The heart is excited by the pacing point, atrium and ventricle successively in each cardiac cycle, accompanied by bioelectric changes, and the graph of various forms of potential changes elicited from the body surface through the electrocardiographic tracer is called electrocardiogram (abbreviated as ECG). ECG is an objective indicator of the process of occurrence, propagation and recovery of cardiac excitation. ECG is an important tool to help determine whether the electrical activity of the heart is normal, and it is the earliest, most commonly used and basic diagnostic method in the diagnosis of coronary heart disease.