Stand Up Paddleboard (SUP) surfing entails riding breaking waves and maneuvering the board on the wave face in a similar manner to traditional surfing. Despite some scientific investigations on SUP, little is known about SUP surfing. The aim of this study was to investigate the physiological response during SUP surfing sessions and to determine how various environmental conditions can influence this response. Heart rate (HR) of an experienced male SUP surfer aged 43 was recorded for 14.9 hours during ten surfing session and synced with on board video footage to enable the examination of the effect of different surfing modes and weather conditions on exercise intensity. Results indicated the SUP surfer's HR was above 70% of HRmax during 85% of each session, with the greatest heart rates were found during falls off the board (~85%HRmax) and while paddling back to the peak (~83%HRmax). Total time surfing a wave was less than 5% with the majority of time spend paddling back into position. Wind speed positively correlated with HR (r2=0.062. p=0.012) and wave height negatively correlated wave caching frequency (r2=0.54, p=0.025). The results highlight the aerobic fitness for SUP surfing, that wave riding, paddling back to the peak and falls appear to be associated with the greatest cardiovascular demand and that environmental conditions can have an effect of physiological response during SUP surfing sessions.