Heart failure is an epidemic of ageing 21st century societies. Despite wide access to modern treatment strategies, many cardiovascular diseases eventually lead to its development. Especially increased survival after acute coronary syndrome contributes to the growing number of patients with heart failure. Despite the use of optimal pharmacological treatment and therapeutic support devices (i.e. cardiac resynchronisation), heart failure manifests in a number of exacerbations, often requiring hospitalisation. The most common cause of symptom exacerbation is volume overload, which might result from disease progression, comorbidities and patient non-compliance, e.g. regarding drug withdrawal or dose reduction. Moreover, each hospitalisation deteriorates prognosis. It is therefore important to optimise pharmacological treatment to improve both survival and symptoms. The main group of symptom-relieving drugs in heart failure are diuretics, which relieve congestionrelated symptoms, improve the quality of life and reduce the risk of further hospitalisations. However, they do not affect prognosis. Moreover, they are not free from limitations, and the desired effect of dehydration can be associated with adverse effects, i.e. impaired renal function. It is therefore important to use the lowest possible doses, sufficient to maintain euvolaemia. The aim of this paper is to summarise the current knowledge concerning the safe use of diuretics, based on the understanding of their mechanisms of action and rules of application in various phases of the disease.