Plant communities are very sensitive to abiotic stresses like cold, heat, flood and drought. Heat stress defined as high temperature than standard temperature, at which biological activities influence. Plant growth is affected by HS in a range of biochemical, physiological, molecular and cellular levels. Cissus quadrangularis is a succulent medicinally important that has adapted for the xerophytic environment. But the extremely high temperature affects the plant physiology. Photosynthesis is the most susceptible process to heat stress. The OJIP analysis shows the minor deviation in PIcs at 45˚C, at this temperature plant increases antenna size. So the specific (ABS/RC, TR/RC and ET/RC) and phenomenological fluxes (ABS/CS, TR/ CS and ET/CS) lifted. While, due to the immense declined in Fm the PS-II and LHCs dissociated at 60˚C, a huge reduction was also observed in PIcs and PIabs at this high temperature. There was no cent percent recovery even after 5 days which shows the acute damage of PS-II.