BAKERSFIELD, Calif. -- Having "gender compatibility" in heart transplants means a lower chance that the heart will be rejected and a better chance of survival.

More than 2,000 patients undergo a heart transplant each year in the United States. The biggest fear for patients after a transplant is that the heart will be rejected.

But rejection risk may be reduced with gender matching between heart donors and recipients.

In a new study, doctors from Johns Hopkins University reviewed records from more than 18,000 heart transplant patients. They found that those who received a heart from a donor with the same gender had a 14 percent lower risk of rejection and a 20 percent reduced risk of death within the first year following the transplant.

Men were more likely than women to receive a matching heart -- 77 percent of men received hearts from male donors compared to 51 percent of women who received hearts donated by women.

Experts theorized that different sizes of male and female hearts may be one reason why gender matching is preferable -- though with donated hearts in short supply, doctors still do not recommend waiting for a gender matched heart to come along.