Cardiac sources of emboli account for over one quarter of all ischemic strokes. Strokes due to cardioembolism are in general severe and prone to early and long-term recurrence. Nonvalvular atrial fibrillation remains the most common cause of cardioembolic stroke. Despite the proven efficacy of oral anticoagulation, it is prescribed for less than half of the patients with risk factors for embolism and no contraindications for anticoagulation. The embolic risk of patent foramen ovale is low except when combined with an atrial septal aneurysm. Aortic arch atheroma as an independent risk factor for ischemic stroke is the subject of ongoing debate. As the risk of embolism is heterogeneous for the various potential cardioembolic conditions, accurate definition of stroke mechanism is very important to guide the most effective therapy.