Researchers say that heart transplant patients’ survival chances improve if the sex of the donor and patient is the same. The study, presented at a New Orleans meeting of the American Heart Assn. articulates that the survival rate goes up by as much as 25 % if the sex of both the donor and the recipient is the same. Although men and women's hearts are anatomically identical, researchers feel it could be due to differences in size or immune systems between the sexes.

Dr. Eric Weiss of Johns Hopkins University in Baltimore who led the study studied UNOS records for 18,240 heart transplants that took place between 1998 and 2007and found that death rates rose by a fifth over average if the donor was a man and the recipient a woman. There was a 13 % lower rejection risk in the first year and a 25 % lower death rate within 30 days of the operation if the transplants matched.

The researchers further found that the most unsuccessful were a woman receiving a "male" heart, while the most successful operations were those involving male recipients and male donors.

Dr Weiss said, "We generally don't assume that organs from male and female donors have inherent differences affecting long-term outcomes, but our data suggest that there are important differences which must be taken into account. Heart size would seem to be the most important factor, beyond that; no-one knows why sex matching is important to transplant survival."

The federally funded study said the worst results were seen in men who received donor hearts from smaller women which indicated that the pumping capacity of the organ is crucial to the success of the procedure. Women who received transplants from males were also likely to reject them possibly due to lingering immune stimulation from earlier pregnancies, experts said.

These findings may not make much of an impact on transplants that are performed due to the sacristy of donor hearts. Dr. Jon Kobashigawa, director of the heart transplant program at the Ronald Reagan UCLA Medical Center said, "Organs are scarce . . . so we must take the next organ that is available."

According to the United Network for Organ Sharing, or UNOS, about 2,200 heart transplants are performed each year, with an additional 2,700 patients are on waiting lists. As three-quarters of all heart transplants are given to men, so by necessity many must receive female organs.

"We hypothesized that we would see a big difference in the short-term survival -- which we did, most likely because of heart-size issues -- but what was interesting was the substantial difference in the long term, as well," Weiss said.

Professor Robert Bonser, a cardiac surgeon from Queen Elizabeth Hospital in Birmingham, said

 "In the UK there are too few donors to make gender matching really practical - the researchers recommend that patients do not wait longer for a same sex organ, and we would certainly agree with that."