Henderson, who is on loan at Bramall Lane from Manchester United, will link up with Gareth Southgate's squad at St George's Park on Wednesday ahead of the upcoming Euro 2020 qualifiers away to the Czech Republic on Friday and Bulgaria on Monday.
The FA said in a statement that the injured Aston Villa keeper Heaton had returned to his club for further assessment on an unspecified injury sustained during Saturday's 5-1 win over Norwich.
Henderson, who has played for England from under-16 to under-21 level, described his call-up as a "dream come true".
"This is what dreams are made of it's a dream come true to receive my first @England senior call up," he said on Twitter.
The 22-year-old is in his second campaign on loan with the Blades, having played a key role in their promotion from the Championship to the Premier League last season.
Henderson has yet to make a senior appearance for his parent club United and has also previously spent time on loan at Stockport, Grimsby and Shrewsbury.
The talented shot-stopper had found himself in the spotlight following an error which gifted Liverpool the winning goal in their recent 1-0 victory at Bramall Lane but overall he has made a solid start to the top flight campaign.
Blades boss Chris Wilder says he always felt the young goalkeeper could quickly put the error against the Reds behind him, suggesting that Southgate had looked at the "bigger picture" surrounding Henderson and credited the player for responding "wonderfully well" from his well-publicised mistake against Jurgen Klopp's title-chasing side.
Meanwhile, Everton's Jordan Pickford and Burnley's Nick Pope are the other keepers in Southgate's squad.