An 80-year-old man developed an acute ischemic stroke and right posterior cerebral artery (PCA) occlusion (figure, A and B). Cardiac and carotid artery ultrasound examinations and 24-hour ECG monitoring did not identify any embolic sources. ECG-gated 4-D CT angiography (CTA) showed a noncalcified plaque with a superimposed mobile component on the ascending aorta (figure, C, and video 1). Virtual angioscopy using the datasets from ECG-gated 4-D CTA showed seaweed-like mobile component in the 3-D view (figure, D, and video 1). This was diagnosed as aortogenic embolism. The antithrombotic therapy was changed from clopidogrel to warfarin with an international normalized ratio of 2.0–3.0, and low-density lipoprotein cholesterol levels were controlled to less than 70 mg/dL by rosuvastatin.