Background: Respiratory failure is not only the most important reason for admission of patients to a medical intensive care unit (ICU), but also a common reason for the deterioration of patients already treated in the ICU. It is a very serious condition associated with significant mortality. Heart failure is a common reason for respiratory failure in both circumstances. Unfortunately, the rapid and accurate differentiation of heart failure from other causes of respiratory failure in the ICU remains a clinical challenge. After evaluation of symptoms, physical examination, arterial blood gases, ECG, and chest x-ray, the clinician is often left with a considerable diagnostic uncertainty that results in misdiagnosis and delay in the initiation of appropriate therapy. In addition, misdiagnosis of heart failure causes morbidity, and increases total treatment time and treatment cost, because treatments for heart failure may be hazardous to patients with other conditions such as chronic obstructive pulmonary disease, and vice verse.