We used intravascular ultrasound (IVUS) to assess the efficacy of the Cappella Sideguard stent system for treating coronary bifurcation lesions. Treatment of bifurcation lesions is associated with restenosis at the side branch (SB) ostium, presumably due to inadequate coverage or stent-vessel wall malapposition. To address these limitations, the Sideguard stent was developed. It includes a balloon-deployed, self-expanding, thin-strut, low-stress, nitinol bare metal stent with anatomic funnel-shaped flaring at the SB ostium. Of 25 patients enrolled in the Sideguard I First-In-Man study, complete serial (after intervention and 6-month follow-up) IVUS images were available in 11 patients. All patients were treated with (1) predilation of the SB, (2) Sideguard stenting in the SB, (3) Cypher stenting in the main vessel, and (4) kissing balloon inflations. The Sideguard stent area at the SB carina increased from 3.9 +/- 1.2 to 4.6 +/- 1.1 mm(2) (p = 0.04), resulting in no change in lumen area (3.9 +/- 1.3 vs 4.0 +/- 1.3 mm(2), p = 0.77) despite an intimal hyperplasia (IH) area of 0.6 +/- 0.7 mm(2). Six patients had minimal IH; the increase in stent area translated into an increase in lumen area of 0.4 +/- 0.6 mm(2); 5 patients had relatively more IH (1.3 +/- 0.4 mm(2)), but the increase in stent area of 1.3 +/- 0.3 mm(2) compensated for the IH, resulting in no lumen decrease. In contrast, the main vessel stent area at the carina did not change (5.9 +/- 1.1 vs 6.0 +/- 1.2 mm(2), p = 0.35). In conclusion, serial IVUS analyses of the self-expanding bare metal Sideguard stent indicate preserved SB ostial lumen dimensions at follow-up due to additional increases in stent area that more than compensated for IH.