Anytime you go have a surgical procedure of any type there is potential for risks and side effects. Since Dr. Heidari is using your fat as the injection, there are fewer opportunities for allergic reactions, but there are still some potential negative reactions to the procedure, which can include but are not limited to:
Altered Sensation in the treatment area
Bleeding (uncommon)
Bruising
Infection (uncommon)
Intravascular injection (injection into a blood vessel - extremely rare)
Minor asymmetry (rare)
Numbness
Swelling