There are multiple varieties of plants that are called heart-leaf. One is a wild ginger that has heart-shaped pungent leaves found in West Virginia to Alabama. Another is an evergreen low-growing perennial having mottled green and silvery-gray heart-shaped pungent leaves found in Virginia to South Carolina. Listera cordata, a variety of herbaceous perennial called heartleaf twayblade, is found in a large portion of the Northeast US and in Canada and is considered endangered.
Houttuynia cordata Thunb is the scientific name for a plant known as heartleaf (or Khowtong) found in Japan, Southern China, and Southeast Asia. It is used as an herb, orally either as part of a tea concoction or pounded to make juice for oral administration, or pounded into a paste for external application. Unlike the heartleaf mentioned by Min and Elayne, however, it is used for a variety of ailments that does not include birth control.
It is possible that the heartleaf tea mentioned in the Wheel of Time is a reference to a now-extinct plant known as silphium or laserwort, a variety of giant fennel that was once found in the city of Cyrene on Africa's northern tip. Among other usages, the plant was most prized for the pregnancy-preventing properties in the heart-shaped fruit.