Bony growths found in heart valves.

A hardened heart valve is like a rusty carburetor on a car: It call stall the machinery.

Working properly, heart valves maintain a one-way flow of blood, preventing backups in one heart chamber or leakage into another. If a valve becomes inflexible and jams, too much blood can flood a chamber and overwork it. If not corrected, faulty valves cause heart murmurs and can lead to heart failure.

Calcium buildups precipitate most heart valve surgery, but researchers now report that many bad valves also have bone growing inside them.

The scientists examined 228 valves removed from 206 patients, whose average age was 68, in heart operations performed between 1994 and 1997. Nearly all of the valves showed some calcification. Surprisingly, 30 of the valves had bony growths, says cardiologist Emile R. Mohler III of the University of Pennsylvania Medical Center in Philadelphia. He presented his team's findings in Atlanta this week at a meeting of the American College of Cardiology.

Evidence of living bone presents a puzzle that goes beyond simple calcium accumulation. "It's startling that cellular organization is involved," Mohler says. "It's bizarre."

A telltale protein called osteopontin appears in these bony valves and sems to play a pivotal role in their ossification. Osteopontin is called a matrix protein because it acts as a framework for bone, which the body builds from calcium.

Osteopontin just doesn't belong in heart valves.

Mohler suggests that genes encoding osteopontin reside innocuously in valve tissues until an injury or other stimulus triggers them. Or, he says, bone tissue may form when stresses in a valve attract roving immune cells called macrophages, which would somehow abet osteopontin production.

"The whole interaction between various cell types and tissues is an area where knowledge is just starting to come on line," says cardiac surgeon John E. Mayer of Harvard Medical School in Boston.

Repetitive trauma has been shown to cause calcium deposits in various parts of the body, he notes. Since heart valves never rest, they make good candidates for such buildup and perhaps ossification.

Doctors remove defective valves from more than 70,000 people a year in the United States. Some are replaced with valves fashioned from pig tissue. These new flaps work, but they can calcify in 8 to 10 years, says Patrice Desvigne-Nickens of the National Heart, Lung, and Blood Institute in Bethesda, Md. Mechanical valves last longer but require the patient to take blood thinners, she adds.

Understanding the cellular machinery in valves and the proteins that drive it may someday enable doctors to unravel faulty valves' declining function and present patients with options other than surgery, Mohler says.