Resistant hypertension is an important public health issue, affecting 10 % of treated hypertensive patients. These patients are the most affected by target organ damage and high cardiovascular event rates, presenting higher levels of morbidity and costs for the national health system. The treatment of resistant hypertension presents a challenging task for the clinicians despite the greater awareness to the issue and the improvements at the level of the treatment of these patients. Indeed, it is unclear whether the administration of 25 mg of spironolactone is the most appropriate therapeutic strategy for these patients. The range of alternative treatments is large and the most recentguidelines are not prescriptive about the best choice of treatmentThe aim of this study is to conduct a randomized controlled triple-blind trial to compare two different approaches for resistant hypertensive patients: routine treatment with 25 mg spironolactone or treatment according to the hemodynamic study- ImpedanceCardiography in the improvement of blood pressure control. This study will be conducted in Hospital Entre o Douro e Vouga E.P.E. (CHEDV), Santa Maria da Feira, Portugal. CHEDV is responsible for supporting 25 Primary Health Care Centers, from where the sample of 982 true resistant hypertensive patients will be taken. We will collect systolic/diastolic blood pressure, mean arterial pressure, pulse pressure, nocturnal hypertension and circadian classification variables with the ABPM at the baseline and 3-months follow up. The higher blood pressure or potassium safety criteria will be collected during the follow-up