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It is now accepted that serotonin can either initiate or aggravate myocardial ischaemia through a vasoconstrictor action and platelet activation. It is therefore possible that substances likely to neutralize the effects of serotonin could be used, without any danger, in humans with ischaemic heart disease. This type of action may therefore be exerted by 5-HT2 antagonists, such as naftidrofuryl. A recent double-blind clinical study has in fact shown that administration of naftidrofuryl versus placebo leads to better exercise tolerance, with an increase in the maximum level and delay in ST segment shift (increase in the threshold of onset of ischaemia). The purpose of this study was therefore to evaluate, in an animal model (pig) of acute myocardial ischaemia (occlusion of the proximal section of the left anterior descending coronary artery), the action of serotonin, naftidrofuryl and a combination of both substances on the following parameters: 1) electrophysiological (sinus heart rate, ST segment shift, T-wave amplitude, duration of monophasic action potentials, intraventricular conduction time); 2) haemodynamic (systolic, diastolic and mean blood pressure, first derivative of rate of increase of left ventricular pressure with time: LV dP/dt max); and 3) biochemical (malonedialdehyde concentration as an index, cell peroxidation index, creatine phosphate and adenosine triphosphate). It was found that co-infusion of serotonin aggravated the myocardial ischemia and that naftidrofuryl exerted beneficial effects on the serotonin-mediated aggravation of myocardial ischaemia.