If you have cardiovascular disease, you may be taking daily aspirin. A child-sized dose of this inexpensive drug can help ward off heart attacks and strokes. But studies show it may do more harm than good in some people-or no good at all. Researchers continue to define who is most likely to benefit from aspirin. Its value appears to depend on your age, gender and whether you have already suffered a heart attack or stroke ("secondary prevention") or simply want to prevent the first one ("primary prevention"). Heres the latest on aspirins preventive powers.