Objectives. This study evaluates the feasibility, reliability and reproducibility of electrocardiogram (ECG)-gated intravascular ultrasound (IVUS) image acquisition during automated transducer withdrawal and automated three-dimensional (3D) boundary detection for assessing on-line the result of coronary stenting. Background. Systolic-diastolic image artifacts frequently limit the clinical applicability of such automated analysis systems. Methods. In 30 patients, after successful angiography-guided implantation of 34 stents in 30 target lesions, we carried out IVUS examinations on-line with the use of ECG-gated automated 3D analyses and conventional manual analyses of two- dimensional images from continuous pullbacks. These on-line measurements were compared with off-line 3D reanalyses. The adequacy of stent deployment was determined by using ultrasound criteria for stent apposition, symmetry and expansion. Results. Gated image acquisition was successfully performed in all patients to allow on-line 3D analysis within 8.7 ± 0.6 min (mean ± SD). Measurements by on-line and off-line 3D analyses correlated closely (r ≤ 0.95), and the minimal stent lumen differed only minimally (8.6 ± 2.8 mm2 vs. 8.5 ± 2.8 mm2, p = NS). The conventional analysis significantly overestimated the minimal stent lumen (9.0 ± 2.7 mm2, p < 0.005) in comparison with results of both 3D analyses. Fourteen stents (41%) failed to meet the criteria by both 3D analyses, all of these not reaching optimal expansion, but only 7 (21%) were detected by conventional analysis (p < 0.02). Intraobserver and interobserver comparison of stent lumen measurements by the automated approach revealed minimal differences (0.0 ± 0.2 mm2 and 0.0 ± 0.3 mm2) and excellent correlations (r = 0.99 and 0.98, respectively). Conclusion. ECG-gated image acquisition after coronary stent deployment is feasible, permits on-line automated 3D reconstruction and analysis and provides reliable and reproducible measurements; these factors facilitate detection of the minimal lumen site.