Leaving a file in can be ok if the tooth was completely cleaned out before the file broke. However, if you are worried about it, ask your dentist to send you to a specialist.
Some teeth have more than one canal, this is normal.
Patients with mitral valve prolapse do not need antibiotics, the AHA changed this guideline about 18 months ago. http://www.americanheart.org/presenter.jhtml?identifier=3047051
has this happend to anyone else and if so what did you do?