Climate change has produced extreme weather effects including prolonged and severe heat waves in regions with traditionally moderate climate. Heat wave is defined as a prolonged period of unusually hot weather, but there is no single accepted definition and multiple indicators of heat exposure are applied in research studies. The process of thermoregulation is complex and relies on central (cerebral) and peripheral mechanisms, mainly sweating and dilation of skin blood vessels. Aging as a physiological process may decrease the effectiveness and capability of heat control making older adults a heat vulnerable population. Heat-related events are perceived as public health issue of major and growing importance and excessive heat exposure contributes to increased morbidity and mortality worldwide. The risk of adverse effects of heat exposure depends on a variety of factors including age, comorbidities, environmental, social and economic factors. The sequelae of heat stress depend on the severity and duration of exposure and may vary from mild to life-threatening symptoms. Heat-related illness includes heat edema (leg swelling), heat rash, heat cramps, syncope (near-fainting or fainting), heat exhaustion and heat stroke. Heat-related illness is often associated with dehydration and electrolyte imbalance. Chronic diseases prevalent in the majority of older adults contribute to vulnerability to heat exposure and heat stress may cause exacerbation of many conditions. Adaptation to heat is one of the mechanisms to reduce heat-related illness. Exercise and physical activity performed in hot environment pose special challenges to physiological reserve. Raising awareness of heat-related illness and preventive strategies among health care workers, vulnerable populations, e.g. older adults and societies is of major importance. Solutions are based on local, national and international collaboration and there are multiple initiatives for urban environments. Climate change demands intensive research to better understand heat exposure challenges and develop effective strategies to minimize the risk for the Earth and its inhabitants.