The authors reviewed current knowledge on occurrence, clinical and prognostic significance, and management of sustained ventricular arrhythmias, atrial fibrillation and bradyarrhythmias in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary interventions (PCI). Cardiac arrhythmias worsen clinical course and prognosis in patients with ST-elevation myocardial infarction undergoing primary PCI. Sustained ventricular arrhythmias developing during or early after PCI and associated with mechanical restoration of coronary flow and reperfusion do not affect mortality, whereas those related to incomplete revascularization and ongoing ischemia are associated with poor prognosis. New-onset atrial fibrillation increases mortality and stroke rates in patients undergoing primary PCI. Among bradyarrhythmias, high-degree atrioventricular block is associated with short- and long-term mortality. Prompt and complete revascularization is the cornerstone of arrhythmia management. Arrhythmias related to reperfusion do not usually require specific treatment, whereas those because of ongoing ischemia, incomplete revascularization and presence of substrate require adequate management including nonpharmacological and pharmacological therapies.