Microvascular reconstructions in the head and neck are usually long operating time procedures. Mechanical anastomotic devices help to reduce operating time and can reduce anastomotic failures avoiding foreign bodies in the lumen of the vessel. One of these systems is the 3M/Precise microvascular anastomotic device, it is a non-absorbable device, however, criticisms of this system have been directed to the fact that pulsation of the vessel wall against a rigid structure could lead to thinning of the vessel wall and aneurysm formation. No aneurysms have been found previously in other experimental models. Our experimental study on the aorta and vena cava of the rat comprises 25 arterial and 25 venous anastomoses. In the arteries, four proximal aneurysms were found, two of these were failures. In the venous anastomoses, no failures were found nor aneurysm formation. The system is very useful for performing clinical end to end venous anastomosis helping to reduce anastomotic failures. Aneurysms have been found in arteries although four different ring sizes were available. The device is less easy to use in them than in veins and sometimes can be difficult to apply, making manual suturing a better choice for clinical arterial anastomosis.