['The intra-aortic balloon pump (IABP) is the most commonly used temporary cardiac assist device. The precise role and the mechanism of any benefit in high-risk patients undergoing percutaneous coronary intervention (PCI) have not been fully determined. We hypothesized that the use of an IABP following PCI in high-risk non-shocked patients would immediately increase coronary blood flow, tissue perfusion and hence preserve left ventricular function.', 'Predefined high-risk, but non-shocked, patients were randomized to either an IABP or no IABP following PCI. Angiography was performed pre-PCI, immediately post-PCI and 10 minutes after the completion of the procedure. TIMI flow grade (TFG), TIMI frame count (TFC) and myocardial blush grade (MBG) were measured. Echocardiographic wall motion index (WMI) was measured on days 1 and 30 following PCI.', 'Of 33 patients, 17 received IABP and 16 did not. At final angiography, the TFG was 2.8 +/- 0.7 and 2.9 +/- 0.3 (p = 0.6), the TFC was 19.9 +/- 23 and 16.9 +/- 16.9 (p = 0.7), and the MBG was 2.5 +/- 0.9 and 2.5 +/- 0.7 (p = 0.9) in the IABP and the no-IABP arms. The WMI on day 1 was 1.7 +/- 0.4 and 1.7 +/- 0.4 (p = 0.7), and on day 30, it was 1.5 +/- 0.4 and 1.5 +/- 0.4 (p = 0.9). There was no difference in the total sum of ST-segment elevation prior to PCI (12.6 +/- 7.7 vs. 13.5 +/- 7.9; p = 0.8), nor in the summed ST change in subsequent electrocardiograms (ECGs) to 48 hours in both of the groups.'] Does intra-aortic counterpulsation improve coronary flow early after PCI in a high-risk group of patients : observations from a randomized trial to explore its mode of action?