Medication reconciliation is a process of comparing the Best Possible Medication History (BPMH) with the medicines prescribed by a physician upon the patient's admission, transfer and discharge from the hospital, followed by the identification and resolution of all discrepancies. The BPMH is described as a comprehensive history of medicines used by a patient prior to hospitalization, and its detailed collection is the basis of successful medication reconciliation process. The aim of this study was to determine the frequency of unintentional discrepancies between medicines prescribed by a physician and those used by elderly patients with cardiovascular diseases prior to hospitalization, as well as their potential to cause clinical deterioration and harm to the patient. The study was conducted at the Department of Cardiovascular Diseases at the Dubrava Clinical Hospital. It included 105 elderly examinees (≥ 65 years), and most of them (90.5%) were hospitalized after emergency admission. Within 24 hours of admission, a clinical pharmacist collected BPMH and compared it with the prescribed pharmacotherapy. Unintentional discrepancies found in doing so were divided according to the type into six groups. Also, considering the potential to cause clinical deterioration and harm to the patient, discrepancies are classified into three classes. Medication discrepancies were found in 96 participants, and 10.2% of these discrepancies had no clinical justification which means that they were unintended. At least one such discrepancie occurred in 38 patients (36.2% of all participants). Omission of the drug is the most frequently detected type of discrepancie, accounting for 70.18% of all unintentional discrepancies. The majority of them (71.93%) were able to cause moderate clinical deterioration, and 10.53% of unintentional discrepancies had the potential to cause serious clinical deterioration. In conclusion, medication reconciliation is a process that, by detecting uintentional discrepancies, plays a major role in increasing safety when using medicines. This is of particular importance for patients with polytherapy, who are therefore significantly more suspectible to the risk of medication errors, and these are often elderly people and patients with cardiovascular diseases. It is therefore necessary to highlight the role of clinical pharmacist who have proven to be the most competent experts in obtaining a complete and accurate medication history.