Examples include polymerase chain reaction (PCR) devices. Example PCR devices comprise a fluid input, a fluid output, and a set of microfluidic channels that fluidly connect the fluid input and the fluid output. 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, and the at least one heating element is to pump fluid to the reaction chamber and from the reaction chamber of each microfluidic channel.