It has been called the demon of all demons. It's destroyed careers. Lives. Killed men who weren't meant to be.

It has taken a man hostage and killed him, and no one ever knew why.

Have you ever known a player who declined late in his career? It's especially obvious in running backs. Their legs are tired and worn. They stopped fighting for yards. It is known as Over-30 Syndrome.

But this, the demon of all demons is widely unknown in the NFL.

It is cardiovascular, also known as heart, disease.

It affects the players that fight the most. That give everything they've got the most. That never back down, always looking for something.

Those players are offensive and defensive linemen.

They are big. Heavy. Tall. Strong. But that's not good enough.

It's especially noticed in offensive linemen. In the 70's, you rarely saw players that were 300 pounds. Now, there's at least one on every roster. Most of these players qualify as obese.

They've got increased heart rates. Many suffer from high blood pressure and high cholesterol. All because they had to make it in the NFL.

Remember Thomas Herrion? The San Francisco 49ers 310-pound guard who died after a preseason game. He was 23 years old.

He didn't deserve to die. He was too big for himself.

He suffered from Ischaemic heart disease (IHD), the most common cause of death in the Western Hemisphere.

It's been ruining lives. And it's killed more than one NFL player.

Remember Damien Nash, the Broncos running back? His heart failed. He was a victim of cardiovascular disease.

There was J.V. Cain, the St. Louis Cardinals tight end. He suffered from "the demon of all demons." His number 88 is retired by the Cardinals.

Why must players do this just for a chance at the NFL? There's no guarantee they'll make it. Are they risking their lives for something that happens to a select few?

The answer is yes. And by doing so, they might as well be killing themselves in the process.