A large study finds that low-dose and regular-strength aspirin seem equally safe and effective for preventing additional heart problems in people who already have heart disease. Aspirin isn’t recommended for healthy people because of a risk of bleeding. But a daily pill can lower the risk of blood clots and heart attacks in folks who already suffered a heart problem. The study sought to find which dose was best. About 15,000 people enrolled themselves and tracked their health online. The lower 81-milligram, or “baby aspirin,” dose was widely preferred. Results were presented at a cardiology conference and published in the New England Journal of Medicine.