The authors study the haemodynamics of the endovenous electrodes of cardiac stimulators (EE) in the light of clinical and plethysmographic investigations. Seven venous thromboses were observed out of 2,000 implantations of stimulators (0.35%). The risk increases with age 7th decade) and the presence of multiple EEs. The comparative plethysmography of a series of 22 normal young subjects and 28 old patients equipped with EEs demonstrates that the deep venous return in the upper limbs of a normal subject is better in a young person and in a dominant limb. In the subject equipped with an EE, distensibility is reduced. Temporary coagulation has its place in the treatment of these phlebites (heparin, followed by calciparin). Surgery to disobstruct or excise EE or fibrinolytics are only required exceptionally.