Heart failure (HF) is defined as a clinical syndrome that can result from any structural or functional cardiac disorder that impairs the ability of the ventricle to fill with and eject blood. The most prominent symptoms of HF are dyspnea, fatigue, and fluid retention. HF affects approximately 5.7 million Americans, and is the primary reason for almost 1 million hospital admissions every year. HF-related hospitalizations are frequently due to fluid overload. Symptoms of fluid overload usually occur late in the course of a patient's decompensation. Monitoring pulmonary fluid status may be valuable for detecting early decompensation, and the adjustment of medical therapy may prevent hospitalization. Intrathoracic impedance cardiography is used to assess fluid accumulation secondary to left-sided HF. It uses a high-frequency, low-amplitude current to measure the resistance to the flow of an alternating electric current.