Objectives: The objective of this study was to examine the changes of blood pressure and hemodynamic parameters after oral magnesium supplementation in patients with essential arterial hypertension. Design: Single arm study on 48 subjects, not blinded, intervention with magnesium oral supplementation. Settings and conduct: The participants took magnesium-supplementation for one month at home and had their blood pressure and hemodynamic parameters measured in hospital settings before and after the intervention. The measurements were performed with sphygmomanometer and impedance cardiography. Participants: Patients with essential arterial hypertension, aged 24-65, with unchanged antihipertensive therapy for at least one month. The exclusion criteria were: renal diseases, gastrointestinal diseases, diabetes mellitus, diseases of adrenal, thyroid and parathyroid glands, angina pectoris, congestive heart failure, aortic coarctation, food and drugs allergy, pregnancy, lactation, myocardial infarction, coronary revascularisation, transitory ischemic attack, oral intake of magnesium supplements in the last one month. Intervention: Daily oral supplementation with 300 mg magnesium in the form of magnesium-oxide granules ("Magnezijum 300 Direkt" , Hermes Arzneimittel GmbH, Germany) during one month at home. Primary outcome measures: blood pressure; heart rate; thoracic fluid content (L/kOhm); stroke volume (the amount of pumped blood during each systole, mL); stroke index ( normalized for body surface area,mL/m2); cardiac output (minute volume of heart, L/min) ; cardiac index (normalized for body surface area, L/(min*m2); acceleration index (peak acceleration of blood flow in the aorta, 1/100/s2); left cardiac work index (normalized for body surface area, kg*m/m²); systemic vascular resistance index (normalized for body surface area, dyn*s*m2/cm5).