Cholesterol Won't Kill You, But Trans Fats Could."

1.Dietary cholesterol is good for your heart -- unless that cholesterol is unnaturally
 oxidized (by frying foods in reused oil, eating lots of polyunsaturated fats, or smoking).
Oxidized lipids contribute to heart disease both by increasing deposition of calcium 
on the arterial wall, and by interrupting blood flow.  

When the researchers added oxysterols to the healthy plasma,
 the proportion of sphingomyelin in the cells increased, as did the uptake of 
calcium.

In the presence of certain salts (in the blood, for example), lipids like sphingomyelin develop a negative charge. This explains the attraction of the positively charged calcium to the arterial wall when high amounts of sphingomyelin are present.

LDL, the so-called "bad cholesterol") when oxidized, it increases the synthesis of a blood-clotting agent, called thromboxane, in the platelets.

The oxysterols enhance calcification of the arteries and promote the synthesis of a clotting agent. And the trans fats and cigarette smoke interfere with the production of a compound, prostacyclin, which normally keeps the blood fluid.