The Bluebirds head to Upton Park on Tuesday night for a third-round clash that will take place just two days after their gut-wrenching 1-0 defeat to Tottenham, thanks to Paulinho's stoppage-time winner.
Spurs boss Andre Villas-Boas has been heavily critical of his side's cup meeting with Aston Villa on Tuesday, their third game in six days.
But Cardiff's clash with the Hammers is the second of their own run of three games in six days, with a Premier League trip to Fulham on the agenda on Saturday.
Mackay is expected to rotate his squad against Sam Allardyce's team, but expects there to be no drop in the full-blooded effort he has seen in their Premier League fixtures.
"I think it is easier for us to retain that work-rate when we have a number of games as there are slightly fewer games than in the Championship, where we regularly played Tuesday and Saturday," he said.
"You now have more time to recover and we have a lot of good people here in terms of our sport science and medical people who help the players recover.
"They are a very fit bunch, they run hard for each other and that will not change over the course of the season.
"No matter what happens in terms of results the effort will not change, it has not for two years and it will not start now.
"We were terrific against a real top team on Sunday.
"We have played three of last season's top six at home and we have absolutely gone at them toe to toe and our fans have seen that and I am very proud of them and going forward I am glad to be in the trenches with them."
Striker Andreas Cornelius is set to miss out again against West Ham as the Dane tries to shake off an ankle injury suffered at Accrington in the last round.
It has been an injury-hit start to the 20-year-old's time with the club, but Mackay has reassured the B£8million forward the pressure will be off him when he returns to full fitness.
"We have sat down and spoken about it to him," said Mackay.
"He realises that so there is no pressure. He is a youngster who has signed a long-term contract at the club, a five-year deal, he is here for a long time and does not need to come here and hit the ground running.
"We have got other forwards. Fraizer Campbell has shown why he is a Premier League player already so it is about nurturing people and bringing them through.
"We did the same with Kim Bo-Kyung last year in terms of adapting and we will do the same with any other players."