It turns out men and women really are different at heart. New research finds that heart transplant patients have better odds of surviving and a lower risk of rejection if they get organs from donors of the same sex.

Size may be part of the explanation. Men's hearts are bigger than women's and have greater pumping capacity. But doctors think differences in hormones or immune systems between the sexes may also play a role.

The study was paid for by the federal government and led by a cardiac surgery researcher at Johns Hopkins University in Baltimore, Dr. Eric Weiss. He presented his findings at an American Heart Association conference in New Orleans.

Unfortunately for many patients, the findings won't make much of a difference. The average wait for a heart is 108 days for women and 119 for men. Three-fourths of heart transplants are done in men, so by necessity, many must receive organs from the opposite sex.