Three new drugs have emerged in the past decade that can reduce deaths from heart attack by one third to one half -- yet fewer than a quarter of heart attack victims reaching U.S. hospitals ever receive treatment with them.

One reason is that doctors remain confused about which drug is the safest and most effective. All three agents must be administered intravenously within hours of the heart attack. They range in price from $200 to $2,200. The drugs are:

Tissue plasminogen activator, or TPA, made by Genentech Inc. Studies show TPA reduces deaths in heart attack patients by 30 percent. The most expensive, it is $2,200 a dose.

Anistreplase, made by SmithKline, Beecham. Introduced in 1990, this drug lowers deaths by some 50 percent in preliminary studies and costs $1,700 a dose.

Streptokinase, made by Hoechst-Rousell Pharmaceuticals Inc. When used with aspirin, streptokinase can reduce the death rate by nearly 50 percent. Used alone, the drug leads to a 25 percent reduction in deaths. The oldest of the drugs -- first approved in 1982 -- it costs $200 a dose.

Most heart attacks happen when a clot suddenly forms in a narrowed artery that carries blood to the heart. The clot cuts off the flow of oxygen-rich blood, suffocating heart-muscle cells and causing permanent, sometimes lethal, damage.

The three drugs are effective because they can dissolve clots and restore blood flow to the heart, thus saving heart-muscle cells and limiting damage to the organ.

About 1.5 million Americans have heart attacks each year, and 300,000 die before they get to the hospital. Most who reach the hospital alive could be candidates for treatment with a clot-dissolver. In Europe, 90 percent of heart attack patients are routinely treated with streptokinase, said Charles Hennekens, a heart researcher at Harvard Medical School. In the U.S., only 20 percent are treated and most of those receive the more expensive TPA.

American doctors believe that TPA opens the blood vessels faster than the other two drugs, and therfore is more effective in limiting damage to the heart, said Eugene Passamani, chief of the National Heart, Lung and Blood Institute's division studying these drugs. TPA also causes fewer complications such as internal bleeding or allergic reactions. At the same time, it slightly increases the risk of a stroke, but the reason for that is not clear.

Streptokinase, which dissolves clots more slowly, can cause severe internal bleeding, allergic reactions and a drop in blood pressure but has not been shown to increase the risk of a stroke. Anistreplase, which combines TPA and streptokinase, can cause any or all of the side effects associated with those two drugs.

There is a growing consensus among heart specialists that it doesn't matter which drug is used as long as some clot-dissolving agent is given to heart attack patients as soon as they get to the hospital. To Harvard's Hennekens, the studies are so convincing that clot-dossolving drugs save lives that not using any of them drugs is substandard care. "If I were having a heart attack right this second," Hennekens said, "I would want to take an aspirin and I would want a {clot-dissolving drug} -- the one that the hospital had on hand and that they could get into my veins the quickest."