Opening clogged arteries with sophisticated balloon probes, zapping diseased heart valves with lasers and determining the personality traits that lead to a heart attack are a handful of the new avenues being pursued by the medical speciality of cardiology. Today's heart specialists are helping people live longer -- and have more options for treatment -- than ever before. More than half a million lives have been saved since 1968, say cardiologists, as a result of changing lifestyles and medical advances. But these advances also raise tough new issues for physicians.

More than 1,800 of these topics were addressed in scientific papers last week at the 57th annual meeting of the American Heart Association (AHA). The largest gathering of cardiologists in the world, the meeting drew more than 16,500 participants -- including some 8,000 physicians and researchers -- to the Miami Beach Convention Center.

Surrounded by more than 2,000 exhibits by companies peddling everything from low-sodium foods to the latest heart-imaging techniques, participants spent five days examining a wide range of heart-focused topics including the effect of calcium on blood pressure, the repair of damaged hearts and the relationship between exercise and heart disease.

Balancing discussion of the advances that are reshaping cardiology was "a whole new concern about the cost of the technology, the ethics and particular conflicts of interest," said AHA president Dr. Antonio Gotto.

Among the challenges facing cardiologists: Teaching the public to recognize heart attack symptoms and seek treatment earlier. New drugs -- such as streptokinase, urokinase and tissue plasminogen activator (TPA) -- can now limit the damage of a heart attack by dissolving blood clots blocking coronary arteries. But the drugs are only effective if used within four to six hours after an attack begins. "Less than one third of patients enter the hospital within four hours after a myocardial infarction heart attack ," says Dr. Burton Sobel, director, Cardiovascular Division at the Washington University Medical School in St. Louis. Doctors also must diagnose faster to use the drugs. Balancing drug benefits against long-term risk. As the life span increases for heart patients, many are taking medication for years, raising questions of long-term side effects. One of the most serious concerns the widely used diuretic hydrochlorothiazide -- which lowers blood pressure, is used by an estimated 20 million Americans and may itself be a risk factor for cardiovascular disease. Men who took hydrochlorothiazide had "an excessive amount of deaths" when compared to a similar group that received the diurectic chlorthalidone, reported University of Minnesota researchers. Studying cholesterol's effect on cardiovascular disease. In the 20 years since researchers began exploring the role of cholesterol in the development of heart and cardiovascular diseases, they've identified 13 lipoproteins -- substances containing fat and protein -- that circulate in the blood in cholesterol-containing complexes.

Using lipoprotein levels as a guide, researchers hope to treat patients long before they develop irreversible symptoms of atherosclerosis -- commonly known as hardening of the arteries and a major cause of heart attack. "Ultimately, we can design more effective therapy and screening for patients" before they have health problems, says Dr. Bryan Brewer, chief of the molecular disease branch at the National Heart Lung and Blood Institute.

One new test -- the thallium stress scan -- is already able to "bring out hidden disease" and help explain why some people with normal levels of cholesterol still develop heart disease, says Dr. Peter Kwiterovich of Johns Hopkins Medical Institutions. In a study of 68 brothers and sisters of heart patients, 19 people had "hidden" coronary artery disease, detected by measuring levels of apoprotein B, a protein that allows cholesterol to circulate in the blood. Yet only two of the 19 people had elevated levels of blood cholesterol.

Another test expected to be available within a year or two, says AHA president Gotto, is a simple fingerprick screening test for cholesterol levels. The test could be used in airports, schools and shopping malls to screen large numbers of people and alert those who need further testing. Exploring the relationship between behavior and heart health. The high-strung, aggressive, hard-driving personality known as Type A is linked by numerous studies to the development of heart disease. Investigators now are attempting to identify the components of Type A personality that prove damaging. "The final answers are not in, but we have some clues," says Dr. Redford Williams of Duke University Medical School.

"Maybe all of the Type A risk can be accounted for by anger and hostility," says Williams, who handed out business cards written in Japanese to see if people would respond with anger or hostility. Type A people who are not hostile or angry and use expressive and enthusiastic speech may even be protected against heart disease, indicates Williams' recent work. Repairing ailing hearts. Heart cells cannot divide after birth, which is why "damage to the heart is so lethal," says Dr. Eugene Morkin of the University of Arizona's Health Sciences Center.

Morkin is studying the contractile proteins in heart muscle, and has discovered striking similarities between proteins in the slow-time muscles -- such as the ones that hold the body upright -- and those in the heart. What makes these muscles different is the molecular control of the proteins -- which could be an important clue to future heart regeneration, he says.

"You've got skeletal muscle to spare," Morkin says. "We might be able one day to graft skeletal muscle to the heart and make it into cardiac muscle." Experiments are already underway in dogs.