The Collaborative International Dictionary of English v.0.48:

Heartseed \Heart"seed`\ (h[aum]rt"s[=e]d`), n. (Bot.)
   A climbing plant of the genus Cardiospermum, having round
   seeds which are marked with a spot like a heart. --Loudon.
   [1913 Webster] heartshaped

WordNet (r) 3.0 (2006):

heartseed
    n 1: herbaceous vine of tropical America and Africa [syn:
         heartseed, Cardiospermum grandiflorum]