Cardiac output monitors are commonly used in clinical practice to detect hemodynamics, so as to make timely adjustments to therapeutic methods, detect various vital signs, and improve prognosis. Cardiac output tester is now mainly used in surgery and intensive care unit. 1. The use of cardiac output tester in surgery can timely and accurately observe the hemodynamic indexes of the operated person, such as heart rate, non-invasive blood pressure, continuous cardiac output and so on. Thus, it can determine the state of the patient during surgery, whether the depth of anesthesia needs to be adjusted, whether the vital signs are stable, whether the fluid supplementation is appropriate, whether the surgical operation is smooth, and whether the cardiac function is perfect. By analyzing the indicators of the cardiac output detector, the physician will carry out the relevant treatment, which will enable the smooth and safe completion of the operation, shorten the hospitalization time, and improve the prognosis. 2. In the intensive care unit, early detection of circulatory changes, timely treatment, timely adjustment of the dose and type of drugs, reduce the occurrence of complications. Overall, the main role of cardiac output tester in the clinic is to detect cardiac function and hemodynamics in time, with a view to improving the prognosis of patients and adjusting surgical and treatment programs in time.