The success of treatment depends not only on the medicine prescribed but also on the patient, especially his or hers adherence to the treatment instructions. Successful treatment requires the consistent administration of prescribed drugs. In previous clinical trials, it was observed that less than 50% of patients comply with the given instructions for the treatment. Factors that affect patients taking medications are: age, gender, socio-economic status, the price of drugs, misunderstood instructions given by health care professionals, forget fulness, length of treatment and the number of medications. The aim of this study was to determine the characteristics of poor compliance in applying the appropriate treatment, and based on the results provide guidance for their improval. A cross-sectional study was carried out involving 135 patients of both sexes aged over 18 years old, hospitalized in the Department of heart disease and blood vessels, University Hospital Split. The criteria for inclusion in this study was prescribed chronic therapy which included taking more than one drug. Data was collected by anonymous questionnaire filled by patients. Analyzing the results we demonstrated a statistically significant gender difference in compliance when taking medical therapy (p = 0.318). Younger patients often stop taking medication compared to older ones in the event of an improvement (p = 0.003) or worsening (p = 0.003) of their clinical condition. Patients favour taking prescribed medication in the morning hours, regardless of duration of treatment (p = 0.043).The number of drugs and the daily dose did not affect compliance (p = 0.14) . The largest number of patients have taken their medication regularly in a period of the first year, while the worst compliance was in a period of one to two years. Study also showed that number of days of hospital stay reduce the patient's compliance (p = 0.029). Furthermore, patients are inclined to change the prescribed dosage of drugs rather than implement the life-style changes they were previously advised by their physician. Sixty-nine percent of patients change the prescribed antihypertensive drug dosage according to values of blood pressure by themselves. The largest number of subjects (64%) talk to their physician about the characteristics and adverse effects of the drug. Research results indicate that patient's compliance can be improved by simpler drug administration, preferably in a single morning dose, and by active participation of patient in his treatment which implies a good communication with the health professionals in order to comprehend the effects of different medication and the meaning of non-pharmacological interventions.