Try to make your explanation fit with the patient's own experience. Keep referring back to what actually happened to him or her. Also, make analogies that a patient can understand--for instance, describing the action of aspirin as making the blood less "sticky" is an idea that most patients can grasp. You could also make the analogy that the lumen of blood vessels can be narrowed by atherosclerotic plaque much as a drainpipe can be clogged by grease and hair-- most people have experienced that at home.