Oliver Sherwood, a two-year-old boy who is suffering from a rare illness that causes chronic high blood pressure, is being kept alive by four daily doses of the erectile dysfunction drug, Viagra.

Viagra helps control Oliver's rare pulmonary hypertension by improving blood flow and opening his veins and capillaries to allow circulation. In adults, this boosts erectile function.

"Viagra is an expensive drug but it's actually one of the cheapest to treat pulmonary hypertension. We're just hoping it'll continue to work as he grows a bit older," Oliver's mom Sarah was quoted by The Daily Telegraph as saying.

Oliver's condition affects around 4,000 people in the United Kingdom. Five children are diagnosed with pulmonary hypertension every year. A simple chest infection could kill an afflicted child like Oliver.