For patients on chronic low-dose aspirin therapy, we will allow a 7 day wash out period. This will only be allowed for patients who are taking aspirin as primary prophylaxis or for unclear indications. Patients who are on aspirin therapy for following indications will be excluded: primary prophylaxis of stroke due to atrial fibrillation, secondary prevention of stroke or myocardial infarction, history of coronary artery disease or peripheral vascular disease. For patients who meet the potential criteria for the 7-day wash out, their medical history will be reviewed by one of the clinician investigators to ensure that it is safe and appropriate to hold the agent.