Advancements in medical technology have prompted the development of leadless cardiac pacemaker (LCP) systems, overcoming challenges associated with conventional pacemakers (CP) utilizing leads. However, the compact size of the LCP necessitates a miniaturized antenna for wireless communication, as it imposes limitations on the available space for the antenna. Thus, this study was conducted to propose a design of a miniaturized fractal-based antenna that operates at 2.40 GHz. An LCP antenna with a small footprint of \(5.31\,{\text{mm}}^{3}\) \((\pi \times 2.6^{2} {\text{mm}} \times 0.25\,{\text{mm}})\) as designed using CST Microwave Studio. The antenna was simulated in free space and inside the heart tissue model to evaluate the performance of the antenna, in terms of reflection coefficient (S11) and realized gain. The performance of the antenna is impacted when simulated inside the heart tissue model compared to in free space. Therefore, the antenna is optimized to achieve satisfactory performance within a heart tissue environment. This optimization involved using a pin shorting technique and optimizing offset of the coaxial-feed cable position. These adjustments are made to bring the resonant frequency from 5.0 GHz to 2.4 GHz, with an \(S_{11}\) of −32 dB and a realized gain of 25.26 dBi. In addition, the proposed antenna will be able to significantly reduce the size of the LCP, making the antenna implantation procedure more noninvasive. As a result, the miniaturized antenna design holds great promise for further advancement of the LCP systems.