Sodium retention refers to the retention of sodium and water in the body, which causes edema, and in severe cases, can even lead to heart failure, mainly due to a decrease in the glomerular filtration rate or an increase in tubular reabsorption. The kidneys are the organs that excrete sodium and excess water. If the glomerular filtration rate decreases or tubular reabsorption increases due to various diseases, such as primary glomerulonephritis and secondary nephropathy, or if the glomerular filtration rate decreases due to decreased renal blood flow in the kidneys because of heart failure or cirrhosis of the liver, edema can be caused by the retention of sodium and water in the extracellular space. In mild cases, edema is only manifested as eyelid edema in the morning, but in severe cases, edema may appear all over the body, and may even lead to acute left heart failure. Patients should seek prompt medical attention and follow the doctor’s instructions.