Contemporary cardiac implantable electronic devices such as pacemakers or event recorders are powered by primary batteries. Device replacement due to battery depletion may cause complications and is costly. The goal of energy harvesting devices is to power the implant with energy from intracorporeal power sources such as vibrations and blood flow. By replacing primary batteries with energy harvesters, reinterventions can be avoided and the size of the total device might be reduced. This paper introduces a device with a lever, which is deflected by the blood stream within the right ventricular outflow tract (RVOT), an attractive site for cardiac pacing. The resulting torque is converted to electrical energy by an electromagnetic mechanism. The blood flow harvester weighs 6.4 g and has a volume of 2 cm3, making the harvester small enough for catheter implantation. It was tested in an experimental setup mimicking flow conditions in the RVOT. The blood flow harvester generated a mean power of 14.39 ± 8.38 μW at 60 bpm (1 Hz) and up to 82.64 ± 17.14 μW at 200 bpm (3.33 Hz) during bench experiments at 1 m/s peak flow velocity. Therefore, it presents a viable alternative to power batteryless and leadless cardiac pacemakers.