OBJECTIVES: To determine the impact of ventricular arrhythmias on hospitalization costs for acute myocardial infarction (AMI) patients. METHODS: A retrospective cohort study design was used. Adult patients with primary diagnosis of AMI (ICD-9 code: 410.x1), between July 2003 and June 2004, were identified from a large retrospective database of approximately five hundred hospitals in the United States. The AMI patients were classified based on secondary diagnosis of ventricular arrhythmia into three groups: AMI with sustained ventricular tachycardia (sustained VT)/ventricular fibrillation (VF) (ICD-9 code: 427.4x, 427.5); AMI with paroxysmal ventricular tachycardia (PVT) (ICD-9 code 427.1); and AMI without ventricular arrhythmia. Multivariate hierarchical regression analysis was performed to study the impact of ventricular arrhythmias on hospitalization costs controlling for patient demographics, hospital characteristics, site of infarction, history of coronary heart disease, co-morbidities and procedures such as percutaneous coronary intervention (PCI), bypass grafts and catheterization. RESULTS: A total of 91,225 patients with primary diagnosis of AMI were identified, of which 8,125 (8.9%) patients had a secondary diagnosis of ventricular arrhythmia, including sustained VT/VF (N=3,004; 3.3%) and PVT (N=5,121; 5.6%). A majority of the AMI patients with ventricular arrhythmia were male (70.2%), Caucasian (73.4%) and ³ 65 years (55%). Average unadjusted hospitalization costs were significantly higher (p<0.001) in AMI patients with sustained VT/VF ($26,524± 29,869) and PVT ($23,447± 27,704) than those for AMI patients without ventricular arrhythmia ($14,449± 16,638). Sustained VT/VF (b=$9220, p<0.001) and PVT (b=$8125, p<0.001) were found to significantly increase hospital costs in AMI patients in the regression model. Presence of diabetes (p<0.001), cancer (p<0.001), procedures like PCI, bypass grafts and catheterization (p<0.001) were the other significant positive predictors of hospital costs. CONCLUSION: Ventricular arrhythmias in AMI patients were associated with significantly higher hospitalization costs. Prevention of ventricular arrhythmia in AMI patients could potentially yield benefits in terms of reduced hospitalization costs.