OBJECTIVE The aim was to assess the effects of chronic regional denervation of the ischaemic myocardium on reperfusion arrhythmias in a model with sparse coronary collateral circulation. METHODS Baseline ventricular refractoriness and epicardial activation times were measured together with reperfusion arrhythmias after 15 min (I-15') or 30 min (I-30') of left anterior descending coronary artery occlusion in 38 barbiturate anaesthetised open chest pigs. Twenty pigs (11 in I-15' and nine in I-30') had a chronic (two week) denervation of the left anteroseptal region, whereas 18 pigs (10 in I-15' and eight in I-30') were sham operated (non-denervated) controls. Denervation was induced by pericoronary application of phenol and verified by absence of adrenergic histofluorescence. RESULTS As compared with controls, denervated pigs showed: (1) longer activation times: 20.3 (SD 5.2) ms v 16.5 (4.6) ms, p < 0.001; (2) slightly longer refractory periods: 348(28) ms v 334(27) ms; (3) a tendency to lower postreperfusion ectopic activity: ectopic beats divided by time free of ventricular tachycardia: 0.13(0.19) v 0.34(0.40) in I-15', and 0.21(0.24) v 0.39(0.44) in I-30'; (4) slower ventricular tachycardia in I-30': 140(29) beats.min-1 v 185(29) beats.min-1, p < 0.009; and (5) comparable incidence of postreperfusion ventricular fibrillation: 4/11 pigs v 2/10 in I-15', and 5/9 v 4/8 in I-30'. CONCLUSIONS Selective chronic denervation of the ischaemic myocardium was unable to protect against malignant reperfusion arrhythmias in hearts with human-like coronary collaterals. This was confirmed at two ischaemic periods known to produce progressive catecholamine accumulation and increased adrenoceptor density in the ischaemic myocardium.