The extra circulating cholesterol, especially the LDL's, are a sign that either (1) the person is eating too much, (2) the person is not exercising enough to "burn" the food that he/she eats, or both. A surplus of LDL's results in a build-up of plaque in the arteries around the body (not just the heart). They can coat the cardiac, peripheral vascular and brain arteries with relatively eccentric plaque, building up over a period of time to create a reduced blood flow.

When the main arteries of the heart are constricted enough, a small thrombus, or blood clot, can clog the remaining opening in the artery and cause the heart muscle cells downstream to lose food and oxygen; this results in a heart attack. In the brain, if the brain arteries are constricted by a build-up...

In the leg, kidneys or other parts of the body, such a plaque build-up, with or without a thrombus, can result in limb ischemia or renal failure.
The best way to treat an LDL/HDL imbalance and to lower total cholesterol is with statins, which can reduce cholesterol and improve the ratio by up to 40% (Holz).

Bibliography

Holz, K. "Intensive Statin Therapy Can Partially Reverse Plaque Build-up in Arteries." 15 March 2006. Medical News Today. 4 August 2007 http://www.medicalnewstoday.com/articles/39470.php.

Naghavi, M. et al. "From Vulnerable Plaque to Vulnerable Patient." Circulation (2003): 1772.

Lipoproteins and Heart Attacks