Cardiovascular diseases are a leading cause of mortality, with limited possibilities for transplantation due to a critical shortage of donor hearts. Replacing the heart with total artificial hearts (TAHs) remains challenging, due to size constraints and energy requirements, among others. To address this, we introduce the LIMO heart, a compact TAH concept based on an efficient soft fluidic transmission system. By reducing actuator volume and enhancing energy transfer, LIMO enables a more compact and efficient design. We developed a soft ventricle prototype using thin-walled pouch actuators that achieve transmission ratios above one via circumferential shrinkage. A fast, cost-effective prototyping method accelerated testing. Experimental results showed high energy transfer efficiency (82 to 91%), and in vitro tests demonstrated promising cardiac outputs of 5.9 liters per minute against aortic pressure and 7.6 liters per minute against pulmonary pressure. These findings represent a step toward a more broadly applicable biventricular soft robotic TAH for treating end-stage heart failure.