Purpose: Heart failure (HF) is a clinical syndrome that is the final stage of most types of heart diseases. Thailand - in the Asia-Pacific region - has an unusually high incidence as the risk factors for heart disease increase due to population structure changes. This article aims to compare the self-care of heart failure clients before and after treatment using case management. Methods: A quasi-experimental research design was employed with 30 clients who were treated at the Khon Kaen University Heart Failure Clinic (KKU-HF) between April 2017 and March 2018. The research tool was a 2-part questionnaire that included demographic data and the comparison of scores of self-care before and after treatment using case management. Inferential statistics and paired t-test were used to analyze the data. Results: Most of the clients were males (80%), and most of them (56.67 %) were around 60 years of age and older. A comparison of scores for knowledge and understanding of self-care, before and after the treatment, showed a statistically significant improvement at the level of 0.05. Self-care behavior had also improved. The general quality of life had improved by up to 66.67%. Conclusion and Implications: The goal of this research study was to reduce the rate of re-hospitalization, the cost of medical treatment, and the death rate of heart failure clients. The findings can be used not only to develop self-care systems of the Khon Kaen University Heart Failure Clinic (KKU-HF) but also for other clinics to adopt.