Diuretic therapy is the cornerstone of the management of fluid overload in heart failure. Resistance to diuretic therapy is the most common reason for treatment failure in patients affected by the combination of heart failure and kidney disease. Currently, there is no way of predicting whether heart failure patients will develop resistance to diuretic therapy and what dose of diuretic is necessary to overcome diuretic resistance. Answering these questions would allow doctors to be able to prescribe an accurate dose of diuretic therapy to prevent diuretic resistance and potential side effects of an excessive diuretic dose. With magnetic resonance imaging, it is possible to measure the kidney sodium (salt) content and observe the diuretic response in patients with heart failure and kidney disease. The investigators speculate that measuring kidney sodium content will allow to predict diuretic response in these patients. The aim of this study is to compare the kidney sodium content in patients with chronic cardiorenal syndrome with and without diuretic resistance. Secondly, in a sample of patients with diagnosed diuretic resistance,the aim will be to observe the changes in kidney sodium content induced by an additional dose of diuretic therapy and to observe whether these changes are associated with a response to diuretic therapy.