Heart failure is when the heart cannot pump blood well. Heart failure is different from cardiac arrest, because the heart is still working. Heart failure can be sudden ("acute"), like after a heart attack, or can come on slowly.
Someone with heart failure can have shortness of breath (which may be worse when they lie flat), waking up breathless at night, swelling of the legs, and needing to urinate often during the night. There are many reasons why someone can get heart failure. Most often, heart failure is caused by heart attacks, high blood pressure, or problems with the heart valves.
A doctor makes a diagnosis of heart failure by asking about the symptoms above, and examining the heart, blood vessels, lungs, liver (for swelling) and legs (for swelling or edema). Other tests to prove the diagnosis are X-rays of the lungs, an echocardiogram (an ultrasound test of the heart) and blood tests.
Heart failure can only be cured with a heart transplant, which is not done often, but most people with heart failure need to take diuretic medicines and other medication (ACE inhibitor, statin). Some people with heart failure are treated with an artificial pacemaker that makes the heart work better.