Predominantly, standard adult heart lung machines are used for pediatric cardiac surgery, only with individually downsized components. Downsizing is limited, e.g., by the required gas exchange surface. To diminish complications, we developed a new miniaturized heart lung machine (MiniHLM) for neonates, with significantly reduced priming volume and blood contact surface by integration of all major system components in one single device. In particular, a rotary blood pump is centrically integrated into the oxygenator and the cardiotomy reservoir with integrated heat exchanger is directly connected. Thus, tubing is only necessary between patient and MiniHLM. A total priming volume of 102 ml could be achieved for the entire extracorporeal circuit (including arterial/venous line), in contrast to the currently smallest device on the market with 213 ml. In first animal experiments with female New Zealand rabbits, the MiniHLM guaranteed both a sufficient gas exchange and an adequate blood flow; 12 rabbits could successfully be weaned off after 1 hour of aortic clamp time. The first in vitro and in vivo tests confirm the concept of the MiniHLM. Its low priming volume and blood contact surface may significantly reduce complications during heart surgery in neonates.