What is coronary heart disease?

Please explain so my 12 year old daughtor can understand.

It's actually one of several things including clogged arteries and hardening of the arteries. Both these restrict blood flow to the heart muscle.

The arteries of the heart (that is, those that feed the heart muscle its oxygen & nutrients) can become clogged with fat or get stiff from smoking & other reasons which can lead to heart attacks b/c the arteries get blocked & the heart doesn't get oxygen, so the heart can stop beating or part of its muscle can die, all of which can lead to death or disability.
RN

All parts of the body need oxygenated blood to keep working. The heart needs this most of all, and supplies itself with this blood through vessels that travel around to different places in the heart. When these vessels become blocked by build up over the years, blood does not reach all parts of the heart. When this happens, parts of the heart may become injured or die, depending on the severity of the blockage.
When a muscle works, it needs more blood. The heart works harder during excercise, and thus, needs more blood. If the blockage in the vessels around the heart is enough to prevent the heart from getting enough blood, the heart will first become sore causing chest pain. This initial damage is reversable as long as the heart doesn't have to work so hard and can get enough blood again. If it doesn't get enough blood still, however, parts of the heart will die and can work again. This is called an MI, or Myocardial (Heart Muscle) Infarctioin (Death). This is a watered down explanation, but I hope it is sufficient. Good luck.

This Patient Guide is written for the loved ones of heart patients who are dealing with the short-term stress that comes with a test, procedure or recent diagnosis of heart disease. It explains why support is so important to a loved one with heart disease. It also offers practical strategies on how to support a loved one while also taking care of yourself.

Coronary heart disease (CHD), also called coronary artery disease (CAD), ischaemic heart disease, atherosclerotic heart disease, is the end result of the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium (the muscle of the heart) with oxygen and nutrients. It is the # 1 killer in the U.S. While the symptoms and signs of coronary heart disease are noted in the advanced state of disease, most individuals with coronary heart disease show no evidence of disease for decades as the disease progresses before the first onset of symptoms, often a "sudden" heart attack, finally arise. After decades of progression, some of these atheromatous plaques may rupture and (along with the activation of the blood clotting system) start limiting blood flow to the heart muscle. The disease is the most common cause of sudden death[1], and is also the most common reason for death of men and women over 20 years of age[2]. According to present trends in the United States, half of healthy 40-year-old males will develop CHD in the future, and one in three healthy 40-year-old women.[3] According to the Guinness Book of Records, Northern Ireland is the country with the most occurrences of CHD.