Intrinsically stretchable electronics represent an attractive platform for next-generation implantable devices by reducing the mechanical mismatch and the immune responses with biological tissues. Despite extensive efforts, soft implantable electronic devices often exhibit an obvious trade-off between electronic performances and mechanical deformability because of limitations of commonly used compliant electronic materials. Here, we introduce a scalable approach to create intrinsically stretchable and implantable electronic devices featuring the deployment of liquid metal components for ultrahigh stretchability up to 400% tensile strain and excellent durability against repetitive deformations. The device architecture further shows long-term stability under physiological conditions, conformal attachments to internal organs, and low interfacial impedance. Successful electrophysiological mapping on rapidly beating hearts demonstrates the potential of intrinsically stretchable electronics for widespread applications in health monitoring, disease diagnosis, and medical therapies.