Results of a new research study point to an interesting finding: heart transplant patients have better odds of survival and a lower risk of rejection if the donor is of the same sex as the recipient.

Size may be at least part of the explanation. Men's hearts are bigger than women's and have greater pumping capacity, and men who get men's hearts fare better. But doctors believe differences in hormones or immune systems between the sexes may also have an impact.

The federally-funded study was led by Dr. Eric Weiss, a cardiac surgery researcher at Johns Hopkins University. He presented his findings Wednesday at an American Heart Association conference.