Acute coronary syndrome continues to represent a significant and destructive event in patients with cardiovascular diseases worldwide. NSTEMI (non-ST-elevation myocardial infarction) is diagnosed through blood tests and an electrocardiogram (ECG). A blood test usually shows increased levels of markers such as creatine kinase-myocardial fraction (CK-MB), troponin I, and troponin T. These markers indicate possible damage to heart cells but are usually milder compared to STEMI (ST-elevation myocardial infarction). However, it is important to note that a heart attack cannot be diagnosed based on blood tests alone. The ECG is crucial in detecting changes in the ST segments, which helps in identifying the presence of a heart attack and its type.The diagnosis and treatment of non-ST segment elevation acute coronary syndrome (NSTEMI) continue to be a challenge in medical practice. Changes in the concentration of cardiac enzymes often indicate possible narrowing of the coronary arteries and are often used as a basis for emergency coronary angiography. Diagnostic methods that enable rapid identification of heart muscle damage are of essential importance for correct diagnosis and efficient implementation of therapy. The aim of this research is to analyze heart muscle deformations as an indicator of ischemia in acute coronary syndrome without ST elevation, and to compare the accuracy of diagnosis by means of two-dimensional examination of myocardial deformation (DSDM) in cases of narrowing of individual coronary arteries in patients with NSTEMI. The research involved 115 subjects with NSTEMI who had not previously been diagnosed with coronary disease, heart failure, structural heart disease, nor had left bundle branch block on the electrocardiogram at admission. All subjects underwent an echocardiographic examination, followed by coronary angiography. Anthropometric, laboratory and echocardiographic parameters were compared between subjects with stenoses and without stenoses, as well as between subjects with narrowing of a certain cardiac artery of interest and other subjects (who had stenoses on other cardiac arteries or did not have narrowing of cardiac arteries). The results showed that many parameters of the regional deformation of the myocardium were related to the narrowing of certain coronary arteries. Also, therapy with calcium channel antagonists, the presence of hyperlipoproteinemia, higher diastolic blood pressure on admission, and deformations of the medial anterior segment of the myocardium (LSMA) were independently associated with narrowing of the left coronary artery (LCA). The diagnostic accuracy of LSMA was 73.4%. The two-dimensional study of myocardial deformation proved to be an extremely successful method in predicting the presence of narrowing of individual coronary arteries in patients with NSTEMI.