Heahmund had not yet met Lagertha (which is probably for the better in this case) but he had seen the venom which Ivar feels for the woman. It had made him vaguely curious about her but it is merely passing thoughts in all honesty.

"I see," Heahmund says and then tilts his head. "Do you think he is actually trustworthy to keep his word, though?"

Heahmund isn't particularly apt to trusting Ivar very much, their truce is tenuous at best.