Blood clotting is very useful, but it is not equally desirable in all parts of our bodies. In particular it seems to me that blood clotting in our hearts (also known as heart attacks) is bad. I am sure there are heart specific antigens. I think it should be quite possible to make anti-heart antibodies and then use the Fab bit to direct anti clotting agents, such as heparin, to the heart. Ideally one would want them to be slow release and not active at first. I think this is possible if the heparin is attached packed in say glycogen (animal starch) which is slowly broken down into glucose. I really wouldn't be amazed if it were possible to protect against heart attacks with slow release heparin directed by anti heart Fab's.

A minor bother is that, since this is a peptide + starch drug it would have to be taken as nose drops not pills, but hey beats having a heart attack.