Boyce has been ruled out for up to nine months with a cruciate ligament tear, while Rowles faces six-to-eight weeks out with a fractured metatarsal.
Hearts boss Robbie Neilson was already planning fresh additions to his squad but admitted the double injury setback has increased the number of players he hopes to bring in.
"With Liam's longer-term injury we need to look at that area,” said Neilson. “It's an area we've always been focusing on to be honest with you.
"We have a couple of targets and hopefully we can get them over the line. We know we need to recruit but the key thing here is always making sure we get quality in.
"We will probably try to add another one or two to that but, again, there is no point just adding numbers. We have young players here like Lewis Neilson, Connor Smith, Euan Henderson and Finlay Pollock. If the guys we look at aren't at a better level than that, then they won't be coming here."
Neilson described Boyce's injury as "hugely disappointing" but insisted now is not the time to discuss the player's future, with the Northern Irishman out of contract next summer.
“The first port of call is to make sure we get him the best surgery possible and to get him rehabbed as quickly as we can,” he added.
“These things (contract talks) will take place in due course. I don’t think we should be sitting here talking about that at this moment in time.”