Due the increasing aging of Brazilian population, it is also increasing the number of chronic diseases´ patients. Adequate information is vital for the patient to take an active role on treatment, increasing treatments´ efficiency. Patient packages inserts may contribute significantly for patients´ information. This research is based on the hypotheses that there is a lack on users´ needs during the patient leaflets design. This lack may cause legibility and readability problems and, consequently, risks by the inadequate use of medicine. The aim of the present research is to contribute to the safe use of medicines from cardiovascular patients. Factors that may prejudice leaflets´legibility and readability were investigated. The research techniques used were: Firstly interview with physicians and patients, and heuristic evaluation of two leaflets of the most widely sold anti hypertensive medicine in Brazil. Then, two questionnaires were applied; one with physicians and the other with patients of the Instituto Nacional de Cardiologia (National Institute of Cardiology), in Rio de Janeiro. Those two questionnaires concerned on the leaflets´ legibility and readability, and its cooperation on the patients´ comprehension of their disease and treatment. Serious legibility and readability problems were identified on the leaflets, generating patient insecurity and unsafe medicines´use.