Percutaneous transvenous mitral commissurotomy (PTMC) is an effective treatment for mitral stenosis, but trans-septal puncture carries a certain risk of complications. There have been few reports on phase-array intra-cardiac echocardiography (ICE) guidance in trans-septal puncture for PTMC, especially in patients with dilated left atrium or distorted anatomy. Herein, we report our preliminary experience with ICE-guided trans-septal puncture in patients with dilated left atrium (>or=5.5 cm) who underwent PTMC. From June 2005 to March 2006, there were nine consecutive patients with symptomatic mitral stenosis and left atrium size larger than 5.5 cm who underwent trans-septal puncture for PTMC with the ICE guidance in this institution by a same operator. The procedural and catheterization results were analyzed. Using ICE guidance, the success rate for trans-septal puncture was 100% for all patients with dilated left atrium (>or=5.5 cm). The trans-septal procedures were free of major and minor complications and the patients were not exposed to contrast medium. Mitral valve area increased significantly from 1.0+/-0.2 cm(2) to 1.9+/-0.2 cm(2). Our preliminary result showed that ICE safely and effectively guided trans-septal puncture for PTMC in patients with dilated left atrium (>or=5.5 cm), thus eliminating contrast medium usage and avoiding unnecessary longer X-ray exposure.