Right-to-left shunts are a well-known cause of cryptogenic ischemic stroke. Transcranial Doppler (TCD) is a highly sensitive, non-invasive screening tool for their detection, including extracardiac shunts. We report the case of a 76-year-old man with a history of dyslipidemia, well-controlled hypertension, and chronic kidney disease, admitted for acute ischemic stroke with language impairment and right upper limb paresthesia. Brain MRI revealed a left temporo-hippocampal infarction due to occlusion of the left posterior cerebral artery. No thrombolysis or thrombectomy was indicated. Initial etiological work-up, including supra-aortic CT angiography, laboratory testing, prolonged cardiac monitoring, and transthoracic echocardiography, did non lead to any significant finding. Transcranial Doppler revealed a large spontaneous right-to-left shunt with a “curtain” pattern of high-intensity transient signals (HITS), without Valsalva maneuver. Transesophageal echocardiography excluded a patent foramen ovale but demonstrated delayed microsgnals via the pulmonary veins. Thoraco-abdomino-pelvic CT angiography identified a pulmonary arteriovenous fistula in the right upper lobe. The patient underwent successful endovascular embolization with a vascular plug, without complications. At 18-month follow-up, complete occlusion of the fistula was confirmed, with no recurrent ischemic stroke. Transcranial Doppler is an excellent first-line screening tool for right-to-left shunts in cryptogenic stroke especially in identifying an extracardiac etiology. A positive TCD should prompt targeted investigations to localize the shunt, particularly to detect pulmonary arteriovenous malformations when transesophageal echocardiography is negative.