Under global warming, heatwaves over India are projected to increase unequivocally. Thus, understanding the causal mechanisms responsible for heatwaves adds immense value to the country's climate change mitigation and adaptation strategies. Although several studies have attempted to understand the physical mechanisms responsible for such events, efforts focusing on South-West India (SWI) are lacking. Here, using long-term observational data (1951-2020) and climate model simulations, we show that the heatwaves over SWI are influenced by major climatic modes, including El Ni & ntilde;o-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and the Indian Ocean Dipole (IOD). The mechanism through which these climatic modes affect the SWI heatwaves is either by weakening of Pacific Walker circulation (ENSO and PDO) or by strengthening the Indian Ocean Hadley circulation (IOD). Further, we found that amongst these climatic modes, PDO explains the majority of the heatwave variability followed by IOD. However, post-1979, the scenario has changed remarkably with ENSO gaining prominence, signifying the strengthening of the relationship between ENSO and SWI heatwaves in the recent past. Overall, our study provides a first insight into the drivers and mechanism of the SWI heatwaves, whose value to designing heatwave adaptation strategies over the ecologically sensitive region can hardly be overemphasised.