Bollywood playback singer KK passed away on May 31.
He had performed at a concert organised by Gurudas College at Nazrul Mancha in south Kolkata for almost an hour on Tuesday evening.
KK reportedly complained about "feeling heavy" and was even sweating profusely during and after his performance.
The Kolkata Police lodged an accidental death report in the case.
His body was sent for post mortem by the cops which has now been completed.
According to a report in Times Now, the post mortem reports confirmed that KK died due to a cardiac arrest.
The report also stated that he had weak lungs and liver.
Meanwhile, KK's mortal remains will be brought back to Mumbai on Wednesday and the funeral will be held in the city on Thursday.
He is survived by his wife and two children.
West Bengal Chief Minister Mamata Banerjee has promised all kinds of support to the singer's bereaved family. His mortal remains are currently at Kolkata's Rabindra Sadan. A gun salute was accorded to the singer.
The vocalist, who is known for his versatility, has sung in different languages including Tamil, Telugu, Kannada, Malayalam, Marathi and Bengali.