Gilead is, by far, the largest income producer in the Nasdaq Biotech Index and today’s warning from the Biotech behemoth which has dragged the stock down 2.8% this morning, is weighing heavily on the exponentially-expanding index. As Bloomberg reports, GILD said nine patients taking its hepatitis C drugs Harvoni or Sovaldi along with the heart treatment amiodarone developed abnormally slow heartbeats and one died of cardiac arrest.