In a child with a pre-existing cardio valvular disease, antibiotic prophylaxis should be administered before a dental extraction so as to prevent:

Premedication with a systemic background Patients with Subacute Bacterial Endocarditis - antibiotic prophylaxis is needed. Patients with abscess - antibiotic therapy. In a child with a pre-existing cardio valvular disease, antibiotic prophylaxis should be  administered before a dental extraction so as to prevent bacterial endocarditis. Reference: Pediatric Dentistry SECOND EDITION, Shobha Tandon; page no 163