James Gandolfini's Fatal Heart Attack Puts Spotlight on Silent Killer

The unexpected death of actor James Gandolfini has put the spotlight on a silent killer: heart disease .

Gandolfini died Wednesday of a heart attack, an autopsy revealed today. But the 51-year-old "Sopranos" star was happy "and healthy" on Father's day, according to family friend Michael Kobold.

"We are all devastated by this loss," Kobold said at a press conference today. "James was a devoted husband, the loving father of two children and a brother and cousin we could always count on."

See pictures of James Gandolfini through the years.

A heart attack occurs when the heart muscle loses its blood supply, often because of a buildup of plaque in the arteries. About 50 percent of men who die unexpectedly from heart disease have no previous symptoms, according to the U.S. Centers for Disease Control and Prevention.

Click here to learn about the risk factors for heart disease.

Heart disease is the No. 1 killer of American men, according to the CDC. At 51, Gandolfini was 13 years younger than the average male heart attack victim, but about one in 10 heart disease deaths occurs in people under the age of 55, the federal agency says.

Obesity is a key risk factor for heart disease, and people with an "apple-shape" body are particularly prone, according to the National Institutes of Health. Gandolfini said he struggled with his weight, especially while playing the role of Tony Soprano.

"When I do get thin, which isn't often, I don't feel the same," he told "Inside the Actors Studio" host James Lipton. "I don't walk the same. He doesn't walk the same. You know, with that lumber."

Gandolfini is survived by his wife, Deborah Lin, his 8-month-old daughter, Liliana, and his 13-year-old son from a previous marriage, Michael.

ABC News' Dr. Richard Besser contributed to this story.