We investigated whether optimized ischaemia monitoring during and after PTCA using continuous recording of standardized 12-lead ECG provides additional information regarding the presence and localization of ischaemia. We studied 50 patients undergoing PTCA who received a total of 173 balloon inflations. Chest leads showed not only significantly more frequent ischaemic changes compared with routine limb lead monitoring (116/173 (67%) vs 88/173 (51%)), but in addition, a significantly earlier appearance of changes; 15.4 +/- 6.2 s after the start of balloon inflation compared with 17.5 +/- 6.8 s in the limb leads. Anginal pain, however, first occurred at 35 +/- 14 s after vessel occlusion in 74/173 (43%) of inflations. The changes in ECG monitoring correlated well with the coronary wedge pressure; at coronary wedge pressures below 20 mmHg, 97% of inflations caused ischaemic ECG changes; at pressures greater than 40 mmHg, changes were noted in only 42% of inflations. PostPTCA, 6/36 (16.7%) patients undergoing continuous 12-lead monitoring showed ischaemic ST-segment changes (asymptomatic in five cases), which helped in decision-making regarding interventional measures. In summary, we have found standardized 12-lead monitoring both during and after PTCA to be more precise and reliable in ischaemia detection and useful for clinical decision making.