The classification of pericardial effusion is divided into four main levels.1. Micro pericardial effusion, the volume of fluid is about 30-50ml, and the depth of fluid in the posterior wall of the left ventricle from the ultrasound is about 2-3mm.2. Small amount of pericardial effusion, the volume of fluid is about 50-200ml, and the depth of fluid in the posterior wall of the left ventricle from the ultrasound is about 5-10mm.3. Moderate amount of pericardial effusion, the volume of fluid is about 200-500ml, and the depth of fluid in the posterior wall of the left ventricle is usually more than 10-20ml. 4. The volume of fluid is about 200-200 ml, and the depth of fluid in the posterior wall of the left ventricle is about 10-20 ml on the ultrasound.4. Large pericardial effusion, the volume of fluid is usually more than 500 ml, and the depth of fluid in the posterior wall of the left ventricle is more than 20 mm.In severe cases, the depth of fluid in the anterior wall of the left ventricle is more than 15 mm, and the whole heart seems to be swimming in the pericardium on ultrasound.