Heart failure is most commonly encountered as congestive heart failure (CHF) a condition that progresses slowly until symptoms begin to show themselves. CHF occurs when the heart can no longer efficiently pump blood throughout the body. It can be caused by ischemic Heart disease, high blood pressure, diseases of the heart's valves, or because the heart becomes enlarged through compensatory exertion. A personal history of previous heart attacks may also cause CHF. Because blood flow is impeded by the inefficient operation of the heart, blood will pool due to gravity in various anatomic sites. Edema of the lower extremities is the most recognizable outward sign of CHF. The feet and legs swell due to the effects of gravity on the circulatory system. The swelling can be mild, resulting in marks remaining in the leg tissues after the removal of footwear or socks, or it can be severe, limiting mobility, and making walking painful. A less obvious form of edema is pulmonary edema, in which blood collects in the lungs, hampering efficient respiration. Obvious outward signs of compromised lung function include shortness of breath, fatigue, and a persistent, unproductive cough. On examination, rales, which are crackling sounds audible through a stethoscope, can be detected in the base of the lungs. In advanced CHF, rales are heard throughout the lungs. The combination of improper circulation and reduced lung function can result in hypoxia, or low oxygen saturation of the red blood cells. In advanced cases, a patient can exhibit cyanosis, which is visible as a blue tint to the nail beds of the fingers and toes. Both of these conditions are commonly treated through the use of prescribed diuretic medication to reduce fluid volume in the body. Diuretics promote the kidneys to remove fluid from the body, reducing blood volume and decreasing strain on the heart through the process. The heart contains four chambers. The two on the right side of the heart receive blood from the rest of the body and pump it into the lungs for oxygen rejuvenation. The two chambers on the left side of the heart receive the blood from the lungs and pump it to the rest of the body to begin the cycle again. CHF can be unilateral or bilateral. Which side of the heart is responsible, or both sides, can be determined by a licensed health care provider familiar with the signs specific to each.