Heart failure is a condition that develops gradually as a weakening heart loses its ability to pump enough blood through the body to take care of the needs of the body’s other organs. In most cases, loss of the ability to pump effectively is a symptom of an underlying problem, such as heart muscle injury due to high blood pressure, a heart attack or coronary heart disease. Coronary heart disease is caused by narrowing of the arteries that supply blood to the heart. (If the blood supply is cut off, the result is a heart attack.)

The term "heart failure" might suggest a complete stoppage of the heart's activity. But the heart doesn't suddenly stop beating. Instead, heart failure most often develops slowly, often over years, as the heart's pumping ability gradually declines and the heart consequently works less efficiently. Many people with heart failure don't realize they even have the condition until years after their heart has begun to weaken. That's because symptoms generally don't show up until the condition is more advanced.

On the next page we'll learn about the symptoms of heart failure in more detail.