Ali was given vaccines and a heartworm injection that lasts for six months. Not quite two hours later, the owner brought him back because he was having a reaction showing hives and redness. Dr Gessner and Dr Knutzen are both experienced ER doctors and immediately gave him a diphenhydramine (Benadryl) and a dexamethasone (steroid) injection. Within 30 minutes after treatment, he was showing great improvement and slowly returning to normal. The picture on the left was before and the picture on the right was during his reaction. Although reactions to vaccines and/or heartworm injections are rare, it is still possible and therefore imperative for an owner to monitor their pet closely for 12-24 hours afterward.