Heart failure is a condition that prevents the body's organs and tissues from getting as much oxygenated blood as they need. Someone whose heart is failing may initially look and feel fine and be completely asymptomatic, showing no signs of anything wrong. But the failing heart's inefficiency will, over time, begin to wreak internal havoc.
For most patients, heart failure eventually makes it hard for them to exert themselves, a condition known as exercise intolerance. They feel fatigue even from light physical activity because the weakened heart cannot deliver enough energy-giving blood to the body. The backup of blood and fluids in the tissues can also cause swelling (edema) in the legs, ankles, and elsewhere. Fluid may collect in the lungs as well, making breathing difficult (dyspnea). These three major symptoms — exercise intolerance, edema (fluid retention and swelling), and dyspnea (shortness of breath) — are classic symptoms of heart failure, though all three may be missing in some patients with the condition. Moreover, these symptoms can have any number of causes and do not necessarily indicate heart failure in a given patient.
Other symptoms of heart failure may include increased urination, abdominal swelling or tenderness, a dry, hacking cough, and sudden weight gain as the kidneys retain more salt and fluids to increase the body's blood volume and compensate for the failing heart.