The study examined the positive predictive value of inpatient and emergency department diagnostic codes for identifying outpatient cases of sudden cardiac death and ventricular arrhythmias in Medicaid and Medicare claims data. Medical records for a random sample of 100 inpatient encounters and 100 emergency department encounters coded with relevant diagnoses were requested and 58% were obtained. First-listed diagnostic codes correctly identified cases 85.3% of the time overall based on criteria in the medical records.