Foregoing researches made on the N/OFQ system brought up a possible role for this system in cardiovascular regulation. In this study we examined how N/OFQ levels of the blood plasma changed in acute cardiovascular diseases. Three cardiac patient groups were created: enzyme positive acute coronary syndrome (EPACS, n = 10), enzyme negative ACS (ENACS, n = 7) and ischemic heart disease (IHD, n = 11). We compared the patients to healthy control subjects (n = 31). We found signifi cantly lower N/OFQ levels in the EPACS [6.86 (6.21-7.38) pg/ ml], ENACS [6.97 (6.87-7.01) pg/ml and IHD groups [7.58 (7.23-8.20) pg/ml] compared to the control group [8.86 (7.27-9.83) pg/ml]. A signifi cant correlation was detected between N/OFQ and white blood cell count (WBC), platelet count (PLT), creatine kinase (CK), glutamate oxaloacetate transaminase (GOT) and cholesterol levels in the EPACS group.Decreased plasma N/OFQ is closely associated with the presence of acute cardiovascular disease, and the severity of symptoms has a signifi cant negative correlation with the N/OFQ levels. We believe that the rate of N/OFQ depression is in association with the level of ischemic stress and the following infl ammatory response. Further investigations are needed to clarify the relevance and elucidate the exact effects of the ischemic stress on the N/OFQ system. Keywords: acute coronary syndrome, angina pectoris, nociceptin/orphanin FQ, ischemic stressMore than a decade now that a new chapter has been opened in the research of the opioid system with Mollereau cloning a new member of the opioid receptor family, which was named opioid receptor like orphan receptor (ORL-1) because it was reminiscent of the opioid receptors on both structural and functional ground (21). A year later the endogenous ligand of the ORL-1 was identifi ed and named nociceptin (for its hyperalgesic effect on mice when administered intracerebroventricularly) and orphanin-FQ, because of the Phe and Gln amino acids on the ends of the peptide chain (21, 22). The ORL-1 receptor was renamed NOP receptor and the nociceptin/orphanin FQ peptide as N/OFQ in the current nomenclature by NC-IUPHAR.