The study deals with temporal and spatial variability of heat waves (HW) in Slovakia within the 1951 – 2010 period. Over the last two decades, the hot spells hit all parts of Slovakia not only with higher frequency, but also with higher intensity. In the most extreme case, the duration of selected HW at selected stations reached almost 50 days in 1992. These severe events had not only the meteorological effects, but also several negative social impacts. The most obvious consequence was excess mortality rate resulted from exposure of population to the heat stress, which was evaluated separately for the 1996 – 2010 period. Long-term positive deviations from expected mortality were found during the period when HW occur in the annual cycle. Relative deviations from the baseline during individual HW reached up to 30 % and year 2010 became mainly significant in this respect. This proved not only to current exeptionality of this topic, but also exemplarly showed the ongoing general increase of weather extremity observed in recent years.