Heart failure affects 5 million Americans and is associated with a tremendous economic burden, leading to 26.7 billion dollars in health care expenditures each year (American Heart Association, American Stroke Association. Heart disease and stroke statistics--2004 update. Available at http://www.americanheart.org/downloadable/heart/1072969766940HSStats2004Update.pdf. Accessed May 4, 2006). Half of these expenditures (nearly $14 billion) are for costly hospital admissions for acute decompensated heart failure. Despite the ubiquity and frequency of acute decompensated heart failure, we have few available techniques to anticipate and correct decompensation. With the advent of the implantable cardioverter defibrillator for the prevention of sudden cardiac death and biventricular pacing for dyssynchrony in heart failure (HF) refractory to medical treatment, indications for implantable devices are expanding in the HF population. Therefore, device-based diagnostic monitoring strategies have the potential to identify patients at risk for decompensation and decrease costly health care uses. The purpose of this review will be to highlight the evidence for diagnostic monitoring in HF, with special emphasis on device-based diagnostic monitoring.