Acute heart failure (AHF) is one of the most important cardiovascular syndromes associated with high cardiovascular morbidity, and is the major cause of admission in emergency departments worldwide. The clinical complexity of AHF has significantly increased, mostly due to the comorbidities: diabetes, arterial hypertension, dyslipidemia, obesity, peripheral vascular disease, renal insufficiency and anemia. Numerous clinical trials have demonstrated a frequent association of AHF and diabetes. Since AHF is a very heterogeneous condition, it is important to identify clinical and laboratory parameters useful for risk stratification of these populations. Hyperglycemia may be one of the most convenient, since it is widely measured, easily interpreted, and inexpensive. Acute coronary syndrome (ACS), arrhythmias and poor compliance to chronic medications are considered to be the most frequent precipitating factors of AHF in diabetics. Several studies identified diabetes as the most prominent independent predictor of morbidity and mortality in both acute and chronic heart failure (HF) patients. The following parameters were identified as the independent predictors of in-hospital mortality in patients with AHF and diabetes: older age, systolic blood pressure <100 mmHg, ACS, non-compliance, history of hypertension, left ventricular ejection fraction (LVEF) <50%, serum creatinine >1.5 mg/dL, marked elevation of natriuretic peptides, hyponatremia, treatment at admission without ACE inhibitors/ARBs/β-blockers, and no percutaneous coronary intervention (PCI) as a treatment modality. The most frequent cause of AHF is ACS, both with ST segment elevation (STEMI) or without (NSTEMI). Hyperglycemia is very common in these patients and although frequently unrecognized and untreated, has a large in-hospital and mortality significance.