Ambient air temperatures (T_a) of <6°C or >29°C have been shown to induce large changes in arterial blood pressure and heart rate in homeotherms. The present study was designed to investigate whether small incremental changes in T_a, such as those found in typical laboratory settings, would have an impact on blood pressure and other cardiovascular parameters in mice and rats. We predicted that small decreases in T_a would impact the cardiovascular parameters of mice more than rats due to the increased thermogenic demands resulting from a greater surface area-to-volume ratio in mice relative to rats. Cardiovascular parameters were measured with radiotelemetry in mice and rats that were housed in temperature-controlled environments. The animals were exposed to different T_a every 72 h, beginning at 30°C and incrementally decreasing by 4°C at each time interval to 18°C and then incrementally increasing back up to 30°C. As T_a decreased, mean blood pressure, heart rate, and pulse pressure increased significantly for both mice (1.6 mmHg/°C, 14.4 beats·min⁻¹·°C⁻¹, and 0.8 mmHg/°C, respectively) and rats (1.2 mmHg/°C, 8.1 beats·min⁻¹·°C⁻¹, and 0.8 mmHg/°C, respectively). Thus small changes in T_a significantly impact the cardiovascular parameters of both rats and mice, with mice demonstrating a greater sensitivity to these T_a changes.