Stent implantation has become a widely accepted endovascular intervention for the treatment of stenosed arteries. This minimally invasive technique has shown excellent results in unbranched arteries. However, stenting bifurcation lesions remains a challenge in coronary intervention as it is associated with a lower success rate. Many different techniques have been proposed in medical practice but all the suggested methodologies have specific limitations. Numerical simulations may help to understand and eliminate the shortcomings of current clinical techniques and devices. In this study, one of the currently applied techniques is analysed which involves the implantation of a stent in the main branch, followed by subsequent inflation of a balloon through the side of the stent. This improves the side branch patency and provides access to the side branch for later stent implantations. The impact of using different balloon sizes and stent designs was investigated. The stent cell through which the balloon is inflated increases considerably and as intuitively expected, using a larger balloon results in a larger opening. Furthermore, it was observed that this procedure may compromise the downstream main branch lumen. These observations correspond well with previously reported results, which were based on in vitro studies. The added value of the proposed numerical model is the ability to study many different techniques/stents, without the need for various expensive stent samples.