In recent decades, we have witnessed the global effects of climate change with increases in average ambient temperatures and the frequency of heat waves. As a result, temperate crop yields have declined and are expected to decline further in the coming years. In flowering plants, the reproductive phase is a developmental stage sensitive to high temperatures with heat-sensitive processes such as pollen development. The response to high temperature involves transcription factors such as phytochrome interacting factors or heat shock factors, chaperone proteins, and phytohormone production, creating a complex response with multiple levels of regulation. However, most of the available data focus on heat shock and pollen development, while information on long-term adaptation in ovule and embryo development is scarce. Using the tools available at the CEITEC Plant Sciences and Cellular Imaging Core Facilities, we have performed a phenotypic analysis of the reproductive phase of wild-type and selected Arabidopsis thaliana mutant plants under different high temperature scenarios. We aim to monitor the thermoresponse of ovules and seeds and to study the molecular mechanisms of this response. Our results provide new data on long-term adaptation to high temperatures during the reproductive phase of plants. Reduced fertility results in reduced seed production and seed quality. Our work provides insight into the effects of high temperatures on seed production and opens the door to a more detailed analysis of the molecular mechanisms responsible for these effects.