 Dr. Slavin, Dr. Ellis, and Dr. Derris all suggested that the amino acid L-citrulline and the micronutrient lycopene, both abundant in watermelon, could improve heart health. Wow. There's a rationale for these ideas, according to Slavin. Scientists know that the kidneys convert L-citrulline into nitrous oxide, which can relax your artery walls. There you go. And lower blood pressure.