An integrated heat exchange system on a microfluidic card. According to one aspect of the invention, the portable microfluidic card has a heating, cooling and heat cycling system on-board such that the card can be used portably. The microfluidic card includes one or more reservoirs containing exothermic or endothermic material. Once the chemical process of the reservoir material is activated, the reservoir provides heat or cooling to specific locations of the microfluidic card. Multiple reservoirs may be included on a single card to provide varying temperatures. The assay chemicals can be moved to the various reservoirs to create a thermal cycle useful in many biological reactions, for example, Polymerase Chain Reaction (PCR) or rtPCR. According to another aspect of the invention, the integrated heat exchanger is an adjacent microfluidic circuit containing fluid that is either independently heated or cooled, or is an exothermic or endothermic material, such that the fluid in the adjacent circuit imparts a change in temperature to the assay fluid in an independent circuit. According to yet another aspect of the invention, a thermal electric cooler (TEC) is used for thermocycling the amplification chamber of a disposable microfluidic card.