November 12 (HealthDay News) -- Matching the gender of heart donors and recipients helps short- and long-term survival of heart transplant patients.

So say U.S. researchers who analyzed data on 18,240 patients who received a heart transplant between 1998 and 2007.

"Heart size would seem to be the most obvious factor; beyond that, no one knows why sex matching is important to transplant survival," study first author Dr. Eric Weiss, a postdoctoral research fellow in the cardiac surgery division at the Johns Hopkins University Medical Institutions, said in an American Heart Association news release.

"In clinical transplantation, 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," Weiss said.

Of the heart transplant patients included in the study, 71 percent were matched by gender to their donor (77 percent of male recipients and 51 percent of female recipients). Twenty-five percent of the patients died after their transplant.

The data analysis showed that matching donor and recipient by gender resulted in:

• 13 percent lower risk of graft rejection within the first year.
• 14 percent lower rate of graft rejection over the study period.
• 25 percent lower 30-day death rate.
• 20 percent lower one-year death rate.

Female recipients who received a heart from a male donor had the greatest risk of death, about 20 percent higher than when a male donor was matched with a male recipient. Male-to-male matching was most successful, with a 61 percent cumulative chance for survival, the study found.

The findings were expected to be presented Nov. 12 at the American Heart Association's annual scientific sessions, in New Orleans.

Despite the findings, the researchers don't recommend that patients wait longer for a same-sex heart.

"Clearly, receiving a heart transplant from a donor of opposite sex is preferable to severe heart failure. If equivalent donors exist for a given patient, our data suggest that picking a sex matched donor may lead to improved short- and long-term survival," Weiss said.

SOURCE: American Heart Association, news release, Nov. 12, 2008