Board Thread:Warhammer 40k General Discussion/@comment-5846164-20130527133906/@comment-6078851-20130620145521

you both make good points and here's another to consider - it's a space marine heart. space marines are known for their 'gigantism'. a single space marine giant heart will be capable of far, far more than regular hearts (i'm not getting into lukas' cardio-pulminary endurance vs 2-hearted marines), and as such it would be capable of safely providing a greater increase in output if it's having to work more.

for my own sidenote: i would think things like dilated cardiomyopathy would be non-existant in gene-enhanced hearts. has there ever been a space marine who had a heart attack? (that's a genuine question, personally i woudn't think so but i don't know.)