Disclosed are compositions and methods for amplification of nucleic acid sequences of interest with greater efficiency and fidelity. The disclosed method relates to isothermal amplification techniques, such as Multiple Displacement Amplification (MDA), where the generation of DNA artifacts is decreased or eliminated. Generally, this can be accomplished by carrying out the reaction at elevated temperature. In particularly useful embodiments of the method, sugars and/or other additives can be used to stabilized the polymerase at high temperature. It has been discovered that generation of high molecular weight artifacts, in an isothermal amplification procedure, is substantially reduced or eliminated while still allowing the desired amplification of input DNA by carrying out the reaction at a higher temperature and, optionally, in the presence of one or more additives. It also has been discovered that isothermal amplification reactions can produce amplification products of high quality, such as low amplification bias, if performed at a higher temperature and, optionally, in the presence of one or more additives.