BACKGROUND This study aimed to determine the association between CD4-positive T-helper (Th) cell subsets, T-helper 1 (Th1) and T-helper 2 (Th2) in patients with acute myocardial infarction (AMI) and the severity of coronary artery disease (CAD) determined by coronary artery angiography. MATERIAL AND METHODS Three groups of patients with AMI who underwent coronary angiography and percutaneous coronary intervention (PCI) included patients with stable CAD (n=35), ST-segment elevation myocardial infarction (STEMI) (n=30), and non-STEMI (NSTEMI) (n=35), and controls (n=33). Measurement of high-sensitivity cardiac troponin T (hs-cTnT) was performed. The numbers of circulating CD4-positive Th1 and Th2 cells were measured using flow cytometry. Plasma levels of interferon-γ (IFN-γ) and interleukin-4 (IL-4) were measured using enzyme-linked immunosorbent assay (ELISA). RESULTS An increase in the Th1 lymphocyte population was associated with more CAD, and an increased Th1/Th2 ratio was found in patients with NSTEMI and STEMI (controls 7.27±2.98; stable CAD 7.58±2.52; NSTEMI 16.62±2.74; and STEMI 22.32±7.35) (P<0.001). The proportion of Th1 cells and the Th1/Th2 ratio increased as the number of affected arteries, the degree of stenosis, and the lesion length increased. At a median follow-up of 18.2 months, patients with CAD and an increased Th1/Th2 ratio had a significant increase in adverse cardiac events compared with patients with a reduced Th1/Th2 ratio (log-rank, P=0.042). CONCLUSIONS An increased ratio of circulating Th1 to Th2 cells in patients with AMI was associated with the severity of CAD determined by angiography.