This study was performed to gain further insight in the heterogeneity of monocytes in the different categories of acute coronary syndrome (ACS), especially between patients with unstable angina pectoris, ST-elevation myocardial infarction (STEMI), and non-ST-elevation myocardial infarction (NSTEMI). For this purpose, blood samples were collected in the acute phase from patients presenting with an ACS. These samples were examined with multiparameter flow cytometry to identify the different monocyte subsets and to analyze the expression of monocyte-associated molecules. Leukocytes, as well as an absolute number of monocytes, showed a clear and significant increase in patients with STEMI. This increase was seen in all subtypes of monocytes. The classical monocytes (CD14++CD16-) of patients with an NSTEMI had a significantly increased CD11b expression when compared to the control group, while these cells showed a decreased expression pattern in STEMI patients. This increased CD11b-expression was also seen in the intermediate monocytes of NSTEMI, while it was almost completely downregulated on the intermediate monocytes of STEMI. Finally, CX3CR1, which is almost exclusively expressed on intermediate and nonclassical monocytes, showed a significant decrease in expression in patients with STEMI. In conclusion, intermediate and nonclassical monocytes have a different immunophenotypic pattern in patients with STEMI versus NSTEMI. These differences reflect the pro-inflammatory state of the monocytes in NSTEMI and can be used as target molecules for novel therapeutic strategies to diminish the migration of proinflammatory monocytes into the myocardial tissue. © 2017 International Society for Advancement of Cytometry.