Actuators based on electro-active polymer (EAP) hydro-gels constitute a very attractive yet poorly explored technology. EAP hydro-gels can expand and contract by several times their original volume by application of a small voltage. They can be engineered to be either porous or non-porous and the pore density and distribution can also be controlled. Their inherent limitations of very low actuation speed and need to operate in an aqueous medium constitute no impediment - and in fact make them particularly suitable - to a host of medical applications, some of them with high economic and societal relevance. The Heart-e-Gel project utilises a micro-system concept based on electrode activation to change the volume of EAP hydro-gels designed for operation in the cardiovascular system. Given the soft and aqueous nature of these gels and considering the need to accommodate for large volume changes, integrating these materials into complete micro-systems poses unique challenges in terms of heterogeneous integration. Heart-e-Gel proposes to target specific medical applications and will require modelling of the micro-system-medical interface as well as assessing the potential of different material, actuation, volume sensing, and system delivery options.