Although some emergency patients entering with severe shock should go directly to the operating room, others require additional tests, radiographs, angiograms, CT scans, and so forth. The conventional approach is to stabilize circulatory function using blood pressure and clinical appearance as criteria, but these may be misleading. Noninvasive hemodynamic monitoring provides an array of data to evaluate cardiac, pulmonary, and tissue perfusion functions in the emergency department, trauma service, operating room, or anywhere in the hospital. Noninvasive systems are becoming more accurate and reliable when compared with the invasive Swan-Ganz thermodilution method for cardiac output. This method allows for evaluation of circulatory deficiencies and titration of therapy to appropriate optimal endpoints.