Heat Waves (HWs) are generally experienced over the core HW zone (CHZ) which comprises of north-west, north, central, east India and north-east Peninsula during the period of March to July with peak during April to June (AMJ) season. During the AMJ season, most of the stations from CHZ showed significant increasing trends in the HW/SHW days. Decade wise, HW/SHW days over CHZ showed noticeable increase in the recent three decades (1991-2000, 2001-2010 and 2011-2020) compared to the previous three decades. Associated with warm (cold) phase of ENSO, an apparent increase (decrease) from average (for the period 1971-2000) has also been observed in the spatial coverage and frequency of HW/SHW days.