Heat is increasingly becoming a problem for human health due to climate change. This is particularly important for cities because of the urban heat island effect. The built-up structure has an influence on the urban climate. Therefore, heat is of interest for spatial planning. Information on the impacts of heat is necessary on a high spatial resolution to adapt to climate change. This thesis investigates the heat related vulnerability in Vienna. The way people are vulnerable to heat was identified based on the state of research. These findings were converted to indicators to analyse the current situation in Vienna. Then, it was compared to the potential future development. Recommendations for urban planning can be derived from this information. The concept of vulnerability examines the sensitivity of the population and location and the exposure by climate stimuli. Vulnerability is a relative term. It was calculated for each location of Vienna in contrast to the rest of the city. The sensitivity was measured by the population density, its age and sex composition and the supply of compensating areas and medical services. The exposure was defined by the average number of summer days per year. Additionally, the adaptive capacity is relevant for the examination of the future. In this study, it was defined by the ability of urban planning to implement adaptation measures. A GIS-based approach was used to examine the differences within the city. This thesis compares the current heat stress with the future development. Therefore, climate scenarios were used. The results show that heat vulnerability is distributed unequally within the City of Vienna. Thus, measures of urban planning are needed. The consideration of heat in the planning process is therefore necessary.