Text: In a trial like the Physicians Health Study (a randomized clinical trial), if a participant develops a heart attack, they would of course be treated, and whether they subsequently took aspirin or not would be determined by the treating physician and the patient. So, in effect they would no longer be active participants. However, keep in mind that many of these studies have multiple endpoints (outcomes, or diseases of interest). In a prospecive cohort study like the Framingham Heart study, if a subject developed a heart attack, they would continue to be followed for other outcomes.