Cardioembolic stroke is generally severe with a high risk for both early and long-term recurrence, requiring early diagnosis. Cardiac CT and MRI are accurate noninvasive alternatives to echocardiography which can demonstrate the potential cardiac source of an embolism and exclude other potential sources. The major sources of cardioembolic stroke include atrial fibrillation, recent myocardial infarction, valvular heart disease, endocarditis, and atrial myxoma. Minor sources of cardioembolism are paradoxical embolism due to patent foramen ovale and atrial septal aneurysm, atrial or ventricular septal defects, calcific aortic stenosis, and mitral annular calcification. The appropriate clinical application of cardiac CT and MRI can allow an exact and timely diagnosis to be made in embolic stroke patients.