The Merci Retriever is the first device for mechanical embolus removal in patients with cerebral ischemia. Use of the device was evaluated using experimental models. Three stroke model systems were created: silicone embolism model with flow system, pig embolism model, and silicone-pig tortuous artery model. The series of extraction procedures (capture, retrieval, and aspiration) was examined in the models under flow control. Coagulated blood clot was adopted as embolic material, to simulate embolic stroke of the carotid or middle cerebral arteries. Retrieval of the clot was successful in only one of six trials in the silicone model of the carotid artery, as the clot easily worked free from the helical tip. Aspiration was successful in three of the six trials. Retrieval was successful in two of four trials in the middle cerebral artery and aspiration was successful in two. Retrieval was successful in all five trials in the pig embolism model, and three of five trials in the silicone-pig tortuous artery model. The Merci Retriever does not always retain the embolism, and the helix tends to distort in acute or rough lumen. Aspiration is not always successful.