Where has the blood clot that caused my stroke come from?

Blood is more likely to form a clot if its normal smooth flow is disturbed and becomes turbulent – rather like the water in a river when it hits rocks. This can happen in the heart if its rhythm becomes irregular in a condition called atrial fibrillation, or in the aorta (the main artery from the heart) or the carotid or vertebral arteries if they become narrowed due to atheroma (a build-up of cholesterol in the wall of the artery) – see Figure 5. If
a blood clot forms in any of these places, it can either block the artery where it has formed or break off and travel up with the blood to the brain (embolism). The clot comes to rest where the artery becomes narrower than the clot, thus preventing any blood getting past it. Sometimes the clot forms in one of the arteries inside the brain itself.