The auxiliary examinations routinely required before cardiac surgery (cardiac surgery) include electrocardiogram, plain X-ray of the heart, and echocardiography. For complex precordial disease, preoperative cardiac catheterization should be performed if necessary to further clarify the diagnosis. For patients with coronary artery disease, coronary angiography should be performed before surgery to clarify the indication for surgery. Electrocardiogram is a graph reflecting the electrophysiological changes in heart activity. ECG is one of the most important methods for clinical diagnosis of the heart, and is especially necessary for the diagnosis of arrhythmias. ECG can indicate atrial and ventricular hypertrophy, thus it is useful for the diagnosis of congenital heart disease, rheumatic valve disease and hypertensive heart disease, etc. It is also valuable for the diagnosis of myocardial infarction, myocarditis and pericarditis. In addition, ECG can reflect the effects of certain electrolytes and drugs on the heart muscle. Plain radiographs of the heart are one of the modern diagnostic tests for cardiovascular diseases. The heart and large blood vessels are the main organs in the mediastinum and form a good contrast with the surrounding inflatable lung tissue. The main functions of X-ray plain radiography are: 1) to objectively show the shape, location, size and other morphological changes of the large blood vessels of the heart and each atrium; 2) to clearly show the thickness and diameter of the blood vessels in the lung, and also to understand the relationship between the heart and the abdominal viscera, which is an important sign for diagnosis. Echocardiography is a non-invasive examination method that applies the principle of ultrasound echo to show the structure of the heart, and can provide a more comprehensive understanding of cardiovascular anatomy and physiological function. It has the advantages of being safe, non-invasive and reproducible. At present, echocardiography has been widely used to diagnose congenital heart disease, heart valve disease, myocardial and pericardial diseases. Because of its unique advantages in examining the structural function of the heart, it has increasingly replaced cardiovascular angiography as a fundamental method of pre-surgical diagnosis. The widespread use of cardiac catheterization echocardiography has greatly improved the diagnostic accuracy of congenital heart disease, and the majority of patients with congenital heart disease can be clearly diagnosed by echocardiography alone before surgery. For patients with significant hemodynamic changes or complex congenital heart disease, further cardiac catheterization is required when the diagnosis is difficult to be evaluated and confirmed by echocardiography alone. This is an invasive procedure that involves the insertion of different functional catheters from the peripheral vessels into the heart chambers and blood vessels for the detection of physiological data and selective angiography to provide precise anatomical and physiological functional information prior to surgery.