Inclusion Criteria:  Patients with renal insufficiency treated with dialysis for a period of at least three months.  Exclusion Criteria:  Patients who experienced myocardial infarction during the three months prior to the start of the study Patients who underwent vascular surgery during the last month Patients who experienced chest pain at rest during the last week before the start of the trial - Patients who had to discontinue dialysis prematurely due to hemodynamic instability.