Examples include polymerase chain reaction (PCR) devices. Example PCR devices comprise a fluid input, ejection nozzles, and a set of microfluidic channels that fluidly connect the fluid input and the ejection nozzles. Each microfluidic channel comprises a reaction chamber, and examples further comprise at least one heating element, where the at least one heating element is positioned in the reaction chamber of each microfluidic channel. The at least one heating element is to heat fluid in the reaction chamber of each fluid channel. The device may eject fluid via the ejection nozzles.