Doppler-based hemodynamic assessment affords a magnitude of diagnostic applications including evaluation of blood flow from the left ventricle. Doppler echocardiography, in the form of transthoracic and transesophageal echocardiography, allows for intermittent evaluation of hemodynamic information including aortic blood flow, global and regional wall motion, and valvular integrity. In the hands of a skilled operator, transthoracic and transesophageal echocardiography provides reliable cardiac output determinations. However, these are not considered routine for hemodynamic monitoring in the critically ill. Neither of the echocardiographic approaches provides the continuously available data needed for ongoing evaluation of response to interventions. In contrast, esophageal Doppler monitoring, a minimally invasive hemodynamic assessment tool, provides the ability for ongoing real-time hemodynamic assessment of the critically ill or compromised patient. This simple-to-use technology requires that a probe, similar in size and shape to a gastric tube, be inserted into the esophagus to obtain measurement of blood flow in the descending aorta. Hemodynamic variables such as cardiac output, preload, afterload, and contractility are measured or derived from the esophageal Doppler monitoring waveform.