Nature is known to be beneficial to health. Epidemiological studies show that living near nature improves self-perceived health and reduces the incidence of morbidity and mortality from disease including cardiovascular disease. To date, however, the mechanisms of how living near nature can improve cardiovascular health outcomes are unclear. The aim of this study was to examine the effect of viewing natural and built-environment scenes on heart rate (HR), blood pressure (BP) and heart rate variability (HRV), as an index of heart rate control. Greater HRV indicates enhanced parasympathetic activity and potentially provides protection against adverse cardiac events. Those with low HRV often have poor prognosis for cardiovascular disease. Our hypothesis was that there would be an increase in parasympathetic activity whilst viewing natural scenes. After ethical approval was attained 29 participants took part (age 39.7±12.1; stature 166.3±8.8 cm; mass 65.8±12.0 kg). Testing took place in the morning in a quiet room (with a constant temperature of 22-23°C). Each participant lay in a supine position for 15 min before HR and BP were continuously recorded using ECG and a Portapres. Five minute recordings were made whilst viewing two collections of slides (each slide shown for 17 seconds) on a 1.8m x 1.8m projector screen. One slideshow contained nature scenes and the second set urban scenes lacking greenery. These were shown in a counter-balanced order with 10 min between slideshows. Two indices of vagal activity were calculated: the root mean square of successive differences in RR intervals (RMSSD) and high frequency (0.15-0.40 Hz) spectral power (HF). Paired t-tests were used to determine significant differences between responses to the two sets of slides. Mean HR (62.6±9.2 and 62.6±9.3 for nature and built respectively);and diastolic BP (59.8±11.0 and 59.8±9.0) were very similar during exposure to nature or built images. Systolic BP was lower during exposure to nature (116.4±10.3 mm/Hg) compared to built (118.4±11.0 mm/Hg). Although not statistically significant the difference was of a moderate effect size of (d=0.3). Indices of vagal activity were both significantly higher when viewing natural versus urban environments: the natural logarithm of HF (lnHF) (6.65±0.8 versus 6.45±0.8 (ln ms2) for nature and built respectively); and RMSSD (50.6±22.1 versus 46.4±18.6 (ms) for nature and built respectively). Vagal control of the heart appears to be enhanced whilst viewing nature. This study shows for the first time a potential mechanism by which viewing nature may induce physiological benefits that are cardioprotective and may explain why living near nature can reduce the incidence of cardiovascular disease.