Most of the marked sex differences in human heart size - and thus differences in such factors as how hard & fast the heart has to work to pump the same amount of blood - occur as a result of the changes each sex goes through in the puberty of adolescence. In/after puberty, the left ventricle - the muscled chamber that pumps blood to the rest of the body - in males is 25-38% larger than in females. Prior to puberty, the difference is much smaller - males only have a 6% advantage prior to age 12 - but 6% is still not nothing.

https://pubmed.ncbi.nlm.nih.gov/7490158/

In pediatric heart transplants

Organ-recipient gender mismatch did not affect mortality for either male or female recipients, though gender-mismatched females had the worst survival compared to gender-matched males, who had the best survival (unadjusted HR 1.26, CI 1.07-1.49; p = 0.005). After adjustment for other risk factors affecting transplant mortality, female recipients had decreased survival compared to male recipients (HR 1.27, CI 1.12-1.44; p = 0.020) and gender matching had no effect. In conclusion, gender mismatch alone did not increase long-term mortality for pediatric heart transplant recipients. However, there may be additive effects of gender and gender matching affecting survival. There are insufficient data at this time

https://pubmed.ncbi.nlm.nih.gov/24119046/