“Various medical conditions can affect a woman’s ability to carry a pregnancy, and at times even threaten her and her child’s life. Some of these conditions include pulmonary hypertension, Marfan’s syndrome and certain congenital problems with the aorta.”
http://www.ncbcenter.org/page.aspx?pid=315
True, all of these are very serious conditions. But none of the them are treated by fallopian tubal ligation. Excision of a fallopian tube is morally justified in the case of removal of a tubal pregnancy, since the tube itself has developed an abnormal condition and is threatening rupture, which might indeed kill the mother as well as her embryo.
However, tubal ligation is not a treatment or cure for pulmonary hypertension, Marfan's syndrome or congenital aortal malformaton. It does nothing whatsoever to heal these conditions.