Cardiac output (CO) is the total volume of blood ejected from one ventricle per minute, also known as cardiac output per minute, or cardiac output for short. In a quiet state, the end-diastolic volume of the normal adult left ventricle is about 125 ml, and the end-systolic volume is about 55 ml. The difference between the two is the stroke volume, which is 70 ml. It can be seen that the ventricle does not eject all the blood that fills the ventricle during each ejection. The percentage of stroke volume to end-diastolic volume is called the ejection fraction. Decreased cardiac output can lead to shock. So what is the diagnosis of decreased cardiac output? The decrease in cardiac output needs to be as low as the cardiac index of 2.5L/(min-m2) before some clinical symptoms appear, such as increased heart rate, smaller pulse pressure, decreased blood pressure (systolic blood pressure below 12kPa), weak pulses in the radial and dorsalis pedis arteries, increased central venous pressure, peripheral vasoconstriction, and cold, pale or cyanotic extremities. Urine volume may decrease to less than 0.5-1ml/kg. At this time, the results of cardiac output and other monitoring: may show cardiac index <2L/(min-m2), beat blood index <25ml/(m2-times), peripheral vascular resistance >1800dyn-s-cm-5, oxygen consumption 100ml/(min-m2), >20mg%.