The Tangerines came from behind to win 3-2 in a five-goal thriller at Tannadice last weekend thanks to a flurry of goals in the last 10 minutes after Saints had enjoyed a 2-0 first-half lead.
Now the Scottish Cup semi-finalists are preparing to go to the capital to face Gary Locke's side and McNamara knows it will be far from easy against the Edinburgh outfit.
McNamara said: "The boys have had a lot of credit for the manner in which they won last week.
"That was rightly so as they had to dig really deep to get the result a nd we'll have to show that kind of commitment and attitude again because Hearts will be very tough opponents.
"Even when we got to 2-2 against St Mirren we didn't settle and we wanted to get the winner.
"Sometimes you have to do that in football because it's always a good thing if you can score late goals.
"Hearts have had a tough time on and off the field this season so will be giving it their all. We're prepared for a hard match and it's one we're all looking forward to."
United face Rangers in the semi-final of the cup at Ibrox in April but McNamara insists they'll be focusing first and foremost on league business.
He said: "Rangers is obviously a big game. However, we have some very important games to play before that.
"They will be getting our full attention. That's the way we always look at things.
"We want to take as many points as possible between now and the end of the season and see where it takes us.
"Rangers in the cup will take care of itself and the league is always our priority.
"We've had some good results in the league in recent weeks which we hope to keep going.
"The lads are in good spirits and are enjoying being part of such a busy spell.
"You always enjoy your football more when you're winning and that's what we hope to do again on Friday.
"Tynecastle is a great place to go and play and hopefully we express ourselves like we can."
- Sports & Recreation