Stage I

You don't really need to remember all of the nitty-gritty details on the various types of cholesterol, just the bottom line:

If your cholesterol levels are out of whack, your heart disease risk is increased. Exactly how cholesterol wreaks havoc is fairly complicated.

All cells have receptors, or "doors," that suck LDL into them. If you have too much cholesterol in your blood, the cells make fewer receptors so they can avoid, quite literally, drowning in cholesterol. This, in turn, leads to more cholesterol floating in your bloodstream. While some of it gets returned to your liver for disposal via the garbage-bearing HDL, some of it stays in the bloodstream. If it hangs around long enough, it may become oxidized. And some of it burrows into your artery walls, where it's even more likely to become oxidized.

To understand oxidation, think about what happens to a metal chair when it's left out in the backyard: It rusts. That's what happens to cells in the body when they're attacked by free radicals -- unstable molecules that damage cells. Free radicals are a by-product of just about any bodily process that involves oxygen.

Why doesn't cholesterol in the bloodstream always become oxidized? Because of wonderful compounds called antioxidants, which do just what their name implies.

Your body has a system to deal with this oxidized cholesterol, dispatching specialized white blood cells called monocytes to gobble it up. If there's too much oxidized cholesterol, however, the monocytes get stuffed. They take on a foamy appearance, hence their new name, "foam cells." These foam cells collect in the blood vessel wall, where they turn dangerous and begin producing free radicals, which further oxidize the cholesterol. Eventually a fatty streak forms -- the dreaded plaque. This is stage I of atherosclerosis, or hardening of the arteries.

Nearly everyone, regardless of their diet or lifestyle, will have at least a low level of damage in their blood vessels by the time they die. And thanks to growing rates of obesity and physical inactivity, even children under 10 are now susceptible.

Stage II

Eventually this mess of cholesterol, foam cells, and other debris builds up, pushing outward from the artery wall. This cholesterol-rich "bump" looks like the pus that develops in an open wound. As with such wounds, white blood cells rush to the site to repair the damage, forming a hard coating, or cap, over it. Meanwhile, the bump continues to grow, eventually becoming so big it narrows the artery, decreasing blood flow and the supply of oxygen and nutrients to the heart. If your heart doesn't get enough oxygen-rich blood, you may feel a squeezing sensation in your chest. This is called angina. It often happens when you exercise, because that's when your heart needs additional oxygen.

Stage III

To understand what may happen next, visualize a rushing mountain stream. As it flows, it knocks aside rocks, plants, and other debris in its way, sending that debris downstream. The same thing can happen in your blood vessels. As the blood flows, it can "rip" the cap off the plaque, letting the pus out just as if you ripped the scab off a wound. The larger the plaque, the more likely it is to rupture. Also, the type of LDL that makes up the plaque could play a role in how easily it bursts; recent research shows that very small, dense LDL particles make these plaques more fragile.

Once a plaque bursts, blood platelets begin sticking to the exposed surface of the ruptured plaque, eventually blocking flow through the vessel altogether and triggering a heart attack or stroke (or, if these blockages occur in the arteries leading to your legs, peripheral artery disease).

Unfortunately, there may not be any warning signs of heart disease before a heart attack occurs, especially in women. Some people experience angina, but others only learn they have a problem when they find themselves in the hospital, hooked up to machines, and a nurse leaning over them telling them about the heart attack they just suffered. That's why it's so important to identify your risk factors, such as high cholesterol, and do what you can to tilt the odds in your favor.