Incubation of porcine coronary artery rings and cardiac muscle tissue in Krebs buffer followed by GUMS analysis of the headspace gas revealed two gases, carbonyl sulfide (COS) and sulfur dioxide (SO2). The gases were identified by characteristic ions obtained by electron ionization, and by comparison of the retention time on a chromatographic column (GS GasPro) with standards of these gases. Stimulation of the arterial rings with acetylcholine and calcium ionophore A23187 increased the levels Of SO2 and COS in the vascular tissue. We also provide evidence that SO2 could originate from disproportionation of a very unstable gas, sulfur monoxide (S=O). We suggest potential origins of these gases and discuss their relevance to endothelium-derived hyperpolarizing factor. (C) 2003 Elsevier Inc. All rights reserved.