We talked last week about the life of famed heart doctor Michael DeBakey. He died this month at age ninety-nine.

Today, we talk about the object of his work. The heart is a complex organ that starts beating a few weeks after conception. At this point the heart is a tube. In the coming days, it grows and bends into the shape of the heart.

Doctor Craig Smith uses a model to explain the heart operation he performed on former president Bill Clinton in September 2004

Later, it divides into four parts. As the heart beats, it pumps blood through these chambers and the blood vessels in the body. The body is estimated to have at least ninety-six thousand kilometers of blood vessels.

That is about the same as two and a half times around the Earth. But blood goes the distance in about twenty seconds on its way back to the heart. Each day the heart pumps about eight thousand liters of blood.

The blood feeds the brain and other organs with oxygen and nutrients. It also carries away carbon dioxide and other waste.

The heart pumps by expanding and contracting of muscle. In a healthy adult, the heart beats an average of seventy-two times a minute -- about one hundred thousand times a day.

A healthy adult heart is about the size of two fists and looks like a piece of red meat. But in overweight people, it can look yellow because of fat.

Rates of heart disease started growing sharply in the second half of the twentieth century. As machines did more and more work, people did less and less. Not only did physical activity decrease, but people started eating more and more processed foods.

Experts say a diet low in fats and high in fruits, vegetables, proteins and whole grains may help reduce the risk of heart disease. At least thirty minutes a day of physical activity, enough to work up a sweat, can also help. Also important to good health is a good night's sleep.

Cardiovascular disease is caused by disorders of the heart and blood vessels. It includes heart attacks, strokes and high blood pressure. The World Health Organization says there are three major causes: tobacco use, physical inactivity and an unhealthy diet.

The W.H.O. says cardiovascular disease is the world's leading cause of death. And it is predicted to remain that way unless more action is taken. Experts estimate that it could kill twenty million people a year by twenty fifteen. An estimated seventeen and a half million people died in the year two thousand five. Around eighty percent of them died in low- and middle-income countries.

And that's the VOA Special English Health Report, written by Caty Weaver. For more health news, go to voaspecialenglish.com. I'm Steve Ember.