Methods and devices for forming an anastomosis utilize a graft vessel secured to a vessel coupling that is fixed to a target vessel without using suture. The vessel coupling may be collapsed for introduction into the target vessel and then expanded to engage the vessel wall. The vessel coupling may be a stent attached to a graft vessel to form a stent-graft assembly. The anastomosis may be carried out to place the graft and target vessels in fluid communication while preserving native proximal flow through the target vessel, which may be a coronary artery. As a result, blood flowing through the coronary artery from the aorta is not blocked by the vessel coupling and thus is free to move past the site of the anastomosis.