Acute circulatory problems, including shock, traditionally have been recognized and treated by subjective symptoms and vital signs (BP and HR) which represent only superficial aspects of the underlying physiology. Shock, however, is objectively diagnosed, evaluated, and treated using invasive physiologic monitoring to measure cardiac function and output, pulmonary function, and tissue perfusion. Multicomponent noninvasive monitoring systems are now being developed to obtain comparable information and provide continuous display of data on-line, in real time. These monitoring systems may be used to evaluate the effectiveness of alternative therapies, and to titrate therapy to achieve optimal physiologic goals that improve outcome.