A few slices of watermelon can have similar effects to Viagra. Their flesh and rind contain citrulline, which can trigger prduction of arginine - an amino acid that benefits the heart and the circulatory system.

Ghimu Patil, a researcher in Texas, said: "Arginine relaxes blood vessels, the same basic effect as Viagra." The nitirc oxide can also help with angina and high blood pressure, according to the study.