The truth is bittersweet: Something in cocoa beans may be good for your heart, but — sigh — that's still no reason to load up on chocolate bars or brownies.

The health potential is real. Cocoa beans have antioxidant compounds called flavanols (search), and a growing pile of scientific research suggests they do good things to blood vessels.

Dolly Sullivan, 60, is a believer. She eats two or three squares of Dove dark chocolate daily and talked her mother into switching from coffee to cocoa.

"I'm a chocoholic. I can't walk by a chocolate store," said Sullivan, who lives in Warwick, R.I. "I've always enjoyed chocolate, but now I have a reason to eat it."

Customers at Neuhaus, a Belgian chocolate shop in Washington's Union Station, like thinking the dark stuff might be healthy, said manager Clementine Loeman.

"That way, they don't feel guilty," Loeman said, adding that chocolate was sometimes considered medicinal when the company began as a pharmacy 148 years ago.

Despite the enthusiasm, flavanols are missing from much of the chocolate on store shelves today. Flavanols make chocolate and cocoa taste bitter, and confectioners have spent years trying to perfect ways to remove the pungent flavor.

"Most chocolate, in fact, isn't flavanol-rich," said Norm Hollenberg, a radiology professor and flavanol expert at Harvard Medical School. "But all chocolate is rich in fat and calories. Chocolate is a delight. It can and should be part of a prudent diet. That means you limit what you take."

Flavanols are found in other foods, such as red wine, grapes, apples and green tea, although cocoa beans are a particularly rich source.

They are so tiny, they cannot be seen, even under a microscope. To find them, it takes sophisticated machinery that seems more appropriate for NASA than a chocolate company's laboratories.

Mars Inc. developed the technology to visualize flavanols on a computer screen. Says Harold Schmitz, the company's chief science officer: "Now we understand cocoa well enough to start to do new things with it."

The company is starting with CocoaVia granola bars, made with a special cocoa powder that retains most of the flavanols. The bars also have plant sterols, which have been shown to help lower cholesterol.

For now, the 80-calorie, 23-gram snack bars are sold only on the Internet. The bars have a satisfyingly rich chocolate flavor, along with a slight but distinct bitter taste.

Mars says its Dove dark chocolates — a 1.3 ounce bar is 200 calories — also contain flavanols.

Researchers are excited by the potential of flavanols to ward off vascular disease, which can cause heart attacks, strokes, diabetes, dementia and hypertension. Vascular diseases are linked to the artery's inability to make a simple but fundamental chemical called nitric oxide. Flavanols appear to reverse that problem.

"The pharmaceutical industry has spent tens, probably hundreds of millions of dollars in search of a chemical that would reverse that abnormality," Hollenberg said. "And God gave us flavanol-rich cocoa, which does that. So the excitement is real."

Hollenberg studied Central America's Kuna Indians, island dwellers near Panama who make their own locally grown, flavanol-rich cocoa.

The Kuna drink a lot of cocoa, and they don't have high blood pressure — except for those who move to the mainland and start drinking commercial cocoa that's flavanol-poor.

Testing the link between flavanols and improved blood flow, Hollenberg fed cocoa with and without flavanols to a study group in the United States and discovered that flavanols seemed to improve blood flow throughout the body.

Another researcher, nutrition professor Carl Keen at the University of California, Davis, has found that flavanols had an aspirin-like effect on blood, among other findings.

Mars contributed to Hollenberg's and Keen's research and countless other projects. The company has collaborated on more than 80 studies.

The company announced last month that its scientists have figured out how to make synthetic flavanols and that major pharmaceutical companies are interested in developing the compounds for prescription drugs.

The health possibilities have many chocolate makers playing up the amount of cocoa in their chocolates, which can also contain sugar, cocoa butter and soya lecithin, an emulsifier that helps the ingredients mix together smoothly.

Next month, Hershey's will release a new Extra Dark chocolate bar containing 60 percent cocoa — more than its 34-year-old Special Dark bar. The cocoa percentage is showing up on many chocolate bars. Neuhaus, for example, has bars with 71 percent, 73 percent and 75 percent cocoa.

"It's great news for consumers that cocoa found in many of their favorite products can contain natural antioxidants," said Hershey's spokeswoman Stephanie Moritz.

Hershey's also recently bought San Francisco-based Scharffen Berger Chocolate Maker, known for its dark chocolate, particularly its Nibby Bar, which has real bits of roasted cacao beans mixed with semisweet chocolate.

Even if you find a flavanol-rich chocolate bar, eating one every day would make you gain weight faster than it would lower your blood pressure, said Abby Ershow, nutrition science officer at the National Institutes of Health's National Heart, Lung, and Blood Institute.

Chocolate lovers don't need a new reason to indulge, Ershow said. "They are going after the taste, which is the main thing chocolate has to offer us all," she said.