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Many landscapes underlying military designated air spaces have been established as national parks, wildlife refuges, or wilderness areas. The juxtaposition of public, wilderness, and military uses has led to questions of compatibility between aircraft and wildlife. We evaluated the effects of simulated low-altitude jet aircraft noise on the behavior and heart rate of captive desert mule deer (Odocoileus hemionus crooki) (n = 6) and mountain sheep (Ovis canadensis mexicana) (n = 5). We measured heart rate and behavior related to the number of simulated overflights per day (range = 1-7) and noise levels (range = 92-112 decibels [dB]) that animals were exposed to. We compared heart rates and behavior of mountain sheep and desert mule deer before, during, and after simulated overflights (n = 112 overflights/season) during 3 seasons. The heart rates of ungulates increased related to dB levels during simulated overflights (P less than or equal to 0.05), but they returned to pre-disturbance levels in 60-180 seconds. Animal behavior also changed during overflights but returned to pre-disturbance conditions in <252 seconds (P less than or equal to 0.005) All animal responses decreased with increased exposure suggesting that they habituated to simulated sound levels of low-altitude aircraft.