Growers need knowledge of how grapevines adjust to heat waves or sudden temperature changes to make informed management decisions. We grew potted grapevines in environmentally controlled growth chambers under different temperature regimes (simulating cool and warm growing seasons) before exposing the vines to sudden temperature changes with maximum temperatures varying from 77°F to 104°F. Photosynthesis measurements showed that grapevines might tolerate a sudden rise in temperature better in a warm than a cool season. During extended heat waves, however, the cool season-acclimated vines recovered faster than the warm season-acclimated vines. To mitigate heat stress in the vineyard with a minimum of water input, we developed a mist-type evaporative cooling system (MECS). The MECS controller activates misting when the canopy temperature exceeds 95°F and the leaves are dry, and stops misting when the canopy temperature declines below 90°F or the leaves are wet. While cooling the west (afternoon sun-exposed) side of the canopy in 2020, we modified the MECS to target the fruit zone in 2021 and 2022. Following the heat waves in those two years, the MECS increased berry size and juice titratable acidity, and reduced wine tannins, compared with untreated control vines. In 2022, the MECS also increased cluster numbers, possibly as a result of enhanced bud fruitfulness. We observed no adverse effects on shoot growth, disease incidence, and physiological disorders. The MECS is compatible with most conventional vineyard management practices except mechanized leaf removal and mechanized pruning. The results from this study will provide growers with science-based information and an innovative tool to mitigate heat stress in vineyards with a minimum of extra water input. This project helps to stabilize grape quality in the Pacific Northwest region, enhancing the industry’s competitiveness in the global market even as recurring heat waves strike this region.