What are the chances i get qt prolongation or abnormal heart rhythm from taking zofran (ondansetron) 4mg tabs for nausea?

Unlikely-but watch : Zofran (ondansetron) can cause qt prolongation which can produce dangerous cardiac arrhythmias and even sudden cardiac death. This would be unlikely at this dosing but should be watched for particularly if low potassium or calcium, or familial qtprolongation (such as in familial sudden cardiac death). Use of other drugs that prolong qt could result in higher likelihood of dangerous qt prolongation w zofran (ondansetron).