3rd degree AV heart block

My 22 year old daughter had a pacemaker 2 yrs. for 3rd degree heart block.  Since then she has had episodes of almost fainting, roaring in ears, periphael vision, nauseous - we had seen the cardiologist, a neurologist for seizures, nothing.  She is wiped out for a day or 2 after.  Saw the cardiologist again, he described the symptons to us and said it was vagal tone and prescribed Zoloft.  My concern is zoloft being a anti-depressent.  Her family dr. questioned the use of zoloft for this.  It has been 2 months and she has not had another episode - they were coming about every 6 weeks.  Has anyone ever heard of this and of zoloft being used for any heart conditions?

Thank you!