Remotely possible. In 1900 a common cause of death was from dental infections. Nowadays with antibiotics not so much. But ignored dental infections can cause rapid swelling cutting off your airway and therefore should not be ignored. Your heart could be affected depending on your general health status.
Low. Infections of the heart are rare, but any infection can spread. It is best to take of it early.
Very low. With today's technology and medical expertise this is very unlikely.
Death by tooth? Yes! The most likely path for a deadly tooth infection is through the brain, not the heart although both are possible. While I can't give the % probability, here's a case that was just in the literature this week: http://www.drbicuspid.com/index.aspx?sec=nws&sub=rad&pag=dis&ItemID=315703&wf=1862#.U3ExOacRDRE.facebook.