In 16 anaesthetized open-chest pigs occlusion of the distal third of the LAD was performed. Local myocardial contractility within and outside the ischaemic area, measured using electromagnetic and ultrasonic probes, arrhythmias and plasma catecholamine concentrations were monitored during 180 min before and 120 min after occlusion of the distal LAD. 5 pigs developed ventricular fibrillation (VF) during phase 1 a of arrhythmias (1-6 min post occlusion) and a further 5 pigs during phase 1 b (10-30 min post occlusion). Segment lengthening within the ischaemic area, measured at the beginning of ventricular ejection, started within a few seconds of ischaemia and reached 11-13.5% of end-diastolic length prior to occlusion after 2 min of ischaemia. Between 2 min and 120 min after the onset of occlusion, no further segment lengthening was observed. There were no significant differences in segment lengthening between VF and non-VF pigs. However, within the VF group, mechanical alterations 2 min after the onset of ischaemia were more marked in pigs developing VF within phase 1 a than those with VF in phase 1 b. VES increased markedly after 50 min of occlusion and seemed to occur independently of further mechanical alterations, VF within the first 30 min of ischaemia often occurred without preceding VES.