<i>Background:</i> This study was aimed at determining the frequency and coexistent patterns of high- and medium-risk cardiac sources of embolism (CSE) as defined by the Trial of ORG 10172 in the Acute Stroke Treatment (TOAST) classification system and at investigating how identified CSE contributed to this classification. <i>Methods:</i> We analyzed data from 2,482 patients with acute cerebral infarctions who registered in the Yonsei Stroke Registry over a 10-year period. Cardiac sources were divided into high- and medium-risk groups based on the TOAST classification. <i>Results:</i> Of the 2,482 patients, 1,130 (46%) underwent echocardiographic studies. At least one CSE was detected in 629 patients (25%). Atrial fibrillation was the most common high-risk CSE. Patent foramen ovale, spontaneous echo contrast and congestive heart failure comprised most of the medium-risk CSE. Atrial fibrillation frequently accompanied coexistent CSE (69%) such as spontaneous echo contrast, congestive heart failure, and left atrial/appendage thrombus, while patent foramen ovale was detected in isolation in more than 90% of the patients. Patients with a high-risk CSE were more likely to be diagnosed with cardioembolism (83%) than patients with only a medium-risk CSE (58%). <i>Conclusions:</i> Our study elucidated the frequency and various coexistent patterns of CSE in Korean stroke patients as defined by the TOAST classification system. In addition, we have demonstrated a higher correlation between high-risk CSE and cardioembolism than with medium-risk CSE and cardioembolism.