Background: Several studies have illustrated the role played by serum glucose levels in cardiovascular morbidity and mortality in general and, more particularly, after an acute coronary event. Aim: The aim of this study was to evaluate the impact of serum potassium and glucose levels on inhospital mortality in patients with ischemic heart disease, who exhibited severe ventricular arrhythmia. Methods: We enrolled 162 consecutive patients who were referred to our institution for an acute coronary event and presented with sustained ventricular tachycardia or ventricular fibrillation during the first 24 hours of hospitalization. Serum potassium and glucose levels were measured in all patients at the onset of tachycardia and after 2, 4, 6, 12, 36, 48 hours. Results: During hospitalization, 23 out of 162 patients died (61% males). Serum glucose levels at the onset of the arrhythmia, as well as after 2, 12, 36 and 48 hours, were higher in the deceased (onset: 228.8 ± 108 vs. 158 ± 68 mg/dl, p = 0.0001, 2 h: 182 ± 109 vs. 149 ± 59 mg/dl, p = 0.03, 12 h: 155.5 ± 72 vs. 128 ± 48 mg/dl, p = 0.025, 36 h: 163.8 ± 63 vs.116 ± 42 mg/dl, p = 0.002, and 48 h: 138 ± 64 vs. 122 ± 42 mg/dl, p = 0.05, respectively), even after adjustment for age, sex, diabetes, left ventricular ejection fraction, type of acute coronary syndrome and site of infarction and medication intake. There was no difference in serum potassium levels between the deceased and survivors. Conclusion: Serum glucose levels at the onset of arrhythmia and 2, 36 and 48 hours later seem to have prognostic significance for in-hospital mortality in patients hospitalized for an acute coronary event, who exhibit severe ventricular arrhythmia.