This study was designed as a randomized controlled experimental type in order to determine the effect of slow breathing exercise applied after the procedure on heart rate, blood pressure and quality of life in patients who underwent Primary Percutaneous Coronary Intervention (PCI) I after the diagnosis of ST Elevation Myocardial Infarction (STEMI). Patients who underwent primary PCI due to STEMI in a Training and Research Hospital in Istanbul will constitute the study population. A sample will be formed with a total of 80 patients, 40 experimental and 40 control groups, selected by computer assisted simple randomization method among volunteer patients who underwent primary PCI and met the inclusion criteria. In this study, slow breathing exercise training will be given to the experimental group by the coordinator. In their home followmup after discharge, they will be asked to do slow breathing exercises for 10 minutes twice a day for eight weeks. Data will be collected using the Patient Information Form, MacNew Heart Disease Health Related Quality of Life Scale, VAS Breath Therapy Satisfaction Evaluation Form, Self-Monitoring Form and Patient Follow up Form. Patients will be seen again during the outpatient clinic examination in the fourth and eighth weeks and the effectiveness of slow breathing exercises will be evaluated with data collection forms.