<b><i>Introduction:</i></b> It is unclear which surrogate of atrial cardiopathy best predicts the risk of developing a recurrent ischemic stroke in embolic stroke of undetermined source (ESUS). Left atrial diameter (LAD) and LAD index (LADi) are often used as markers of left atrial enlargement in current ESUS research, but left atrial volume index (LAVi) has been found to be a better predictor of cardiovascular outcomes in other patient populations. <b><i>Objective:</i></b> We aim to compare the performance of LAVi, LAD, and LADi in predicting the development of new-onset atrial fibrillation (AF) and stroke recurrence in ESUS. <b><i>Methods:</i></b> Between October 2014 and October 2017, consecutive patients diagnosed with ESUS were followed for new-onset AF, ischemic stroke recurrence, and a composite outcome of occult AF and stroke recurrence. LAVi and LADi were measured by transthoracic echocardiogram; “high” LAVi was defined as ≥35 mL/m² in accordance with American Society of Echocardiography guidelines. <b><i>Results:</i></b> 185 ischemic stroke patients with ESUS were recruited and followed for a median duration of 2.1 years. Increased LAVi was associated with new-onset AF detection (aOR 1.08; 95% CI 1.03–1.14; <i>p</i> = 0.003) and stroke recurrence (aOR 1.05; 95% CI 1.01–1.10; <i>p</i> = 0.026). Patients with “high” LAVi had a higher likelihood of developing a composite of AF detection and stroke recurrence (HR 3.45; 95% CI 1.55–7.67; <i>p</i> = 0.002). No significant association was observed between LADi and either occult AF or stroke recurrence. <b><i>Conclusions:</i></b> LAVi is associated with new-onset AF and stroke recurrence in ESUS patients and may be a better surrogate of atrial cardiopathy.