A system for use in accessing and treating a carotid artery, said system comprising: an arterial access device comprising a sheath having an internal lumen, the sheath adapted to be introduced into a common carotid artery via a transcervical incision and receive blood flow into the internal lumen from the common carotid artery; a shunt fluidly connected to the arterial access device, wherein the shunt has an internal lumen that provides a pathway for blood to flow from the internal lumen of the sheath toward a return site; a hemostasis valve located at the proximal end of a proximal extension, the hemostasis valve adapted to inhibit blood flow out of the internal lumen of the proximal extension while allowing catheter introduction into the internal lumen of the proximal extension and into internal lumen of the sheath; a tube coaxially received over a portion of an exterior of the distal section of the sheath such that a portion of the distal section of the sheath is covered by the tube and a portion of the distal section of the sheath is exposed, the tube thereby being arranged to limit insertion of the sheath into a carotid artery to the exposed portion characterized by said proximal extension having a distal end connected to a proximal end of the sheath at a connection location, the proximal extension having an internal lumen in fluid communication with an internal lumen of the sheath; and a flow control assembly coupled to the shunt and adapted to regulate blood flow through the shunt between at least a first blood flow state and at least a second blood flow state, wherein the flow control assembly includes one or more components that interact with the blood flow through the shunt. an arterial access device comprising a sheath having an internal lumen, the sheath adapted to be introduced into a common carotid artery via a transcervical incision and receive blood flow into the internal lumen from the common carotid artery; a shunt fluidly connected to the arterial access device, wherein the shunt has an internal lumen that provides a pathway for blood to flow from the internal lumen of the sheath toward a return site; a hemostasis valve located at the proximal end of a proximal extension, the hemostasis valve adapted to inhibit blood flow out of the internal lumen of the proximal extension while allowing catheter introduction into the internal lumen of the proximal extension and into internal lumen of the sheath; a tube coaxially received over a portion of an exterior of the distal section of the sheath such that a portion of the distal section of the sheath is covered by the tube and a portion of the distal section of the sheath is exposed, the tube thereby being arranged to limit insertion of the sheath into a carotid artery to the exposed portion characterized by said proximal extension having a distal end connected to a proximal end of the sheath at a connection location, the proximal extension having an internal lumen in fluid communication with an internal lumen of the sheath; and a flow control assembly coupled to the shunt and adapted to regulate blood flow through the shunt between at least a first blood flow state and at least a second blood flow state, wherein the flow control assembly includes one or more components that interact with the blood flow through the shunt. <EOS>