A low ejection fraction is defined as an ejection fraction that is lower than the normal percentage. Patients who present with cardiac insufficiency often have a reduced ejection fraction. The chance of sudden death from malignant arrhythmias increases significantly when the ejection fraction drops below 35%. What tests should be done for low ejection fraction? 1. Doppler echocardiography Doppler echocardiography has many red blood cells within the blood, which reflect and scatter ultrasound and can be considered as a tiny source of sound. The probe is placed in the rib cage and does not move while emitting 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. 2, two-dimensional echocardiography two-dimensional echocardiography, also known as cross-sectionalechocardiography, referred to as two-dimensional ultrasound, will be reflected back from the body echo signal in the form of light dots to form a cross-sectional image, also known as brightness modulation (Brightnessmode). It is a basic examination method that shows the morphology, spatial location and continuous relationship of each structure of the heart in a clear, visual and real-time manner. Echocardiography has been widely used as a non-invasive test for heart disease, but M-mode echocardiography is limited by the fact that it can only record one-dimensional images of cardiac structures. Two-dimensional echocardiography, a real-time cross-sectional image of the heart, overcomes the limitations of M-mode and is more suitable for evaluating myocardial contraction abnormalities and estimating ventricular function. 3, cardiovascular angiography Cardiovascular angiography is one of the most important tools for diagnosing cardiovascular disease. It is a relatively complex and special examination method with certain risks and requires strict indications. Right heart angiography: preoperative definite diagnosis of congenital heart disease. To determine the nature of the heart murmur in order to guide the treatment. For those who have reappeared symptoms after heart surgery and need to undergo further surgery. Left heart angiography: mitral stenosis or insufficiency. Aortic stenosis or insufficiency. Congenital heart disease. Primary cardiomyopathy. Left ventricular ventricular wall tumor, etc.