Reef building corals depend on symbiotic algae, which live inside of their tissue and provide most of the coral's energy through photosynthesis. One of the biggest threats to the survival of corals today are marine heatwaves that often result in the loss of their symbiotic algae in an event called coral bleaching. In some coral bleaching events, adjacent colony pairs have been shown to be bleaching-resistant or bleaching-susceptible, despite being of the same species and experiencing the same environmental conditions. What determines these bleaching responses, and long-term impacts of marine heatwaves on all corals regardless of their resistance or susceptibility to bleaching is still unknown. This project utilizes histology techniques to determine tissue integrity of bleaching-resistant and bleaching-susceptible corals before and during a severe marine heatwave. Coral samples were collected from Kāne’ohe Bay, Hawaii in July and October, before and during the 2019 marine heatwave, along with images of the colonies to determine their phenotypic bleaching response. The samples were processed for histology using H&E staining and microscopic image analysis. Results indicate that tissue degradation is present in both bleaching-susceptible and bleaching-resistant coral colonies during the heatwave, regardless of bleaching phenotype. Notably, corals that appear unaffected during bleaching events, may experience significant stress from marine heatwaves including the loss of tissue integrity that could have long-term consequences to coral health. Further analysis is required to investigate the long-term health effects of bleaching events in order to preserve and better predict the future of coral reef ecosystems.