May 8, 2007 -- Baby aspirin may be the best aspirin dose for heart health, according to a new research review. A single pill of baby aspirin contains 81 milligrams of aspirin. That's about a quarter of the 325-milligram dose in an adult aspirin pill. The new research review states that in the U.S., the most commonly prescribed aspirin dose for heart health is 81 milligrams per day.