An ingredient in a scorpion's sting could be used to stop heart bypasses failing, researchers say.
Margatoxin, from the venom of the Central American bark scorpion, proved effective in preventing a complication.
New blood cells can grow inside blood vessels, restricting blood flow and eventually causing a graft to fail.
Heart experts said the University of Leeds study, published in the journal Cardiovascular Research, was "promising".
The British Heart Foundation says around 25,000 coronary artery bypass grafts are carried out each year in the UK and, if successful, last around 10 to 15 years.
A common complication of heart bypass is neointimal hyperplasia, which is the blood vessel's response to injury.
It triggers a thickening of the lining of the vessel, blocking it.
When a vein is grafted onto the heart during a bypass procedure, the injury response kicks in as the vein tries to adapt to the new environment and different circulatory pressures.
The growth of new cells helps to strengthen the vein, but internal cell growth restricts blood flow and ultimately leads to the graft failing.
In the study, the researchers tested a range of compounds, and found the scorpion toxin was the most effective.
The Central American bark scorpions are native to Central and South America and are usually about 5cm to 8cm long.
The venom is not deadly to humans but has a painful sting which causes swelling and tingling.
The toxin works by blocking a potassium ion channel called Kv1.3 - a pore in the cell membrane that opens and closes in response to electrical signals and assists the delivery of calcium ion, which takes messages between cells.
Professor David Beech, of the University of Leed's faculty of biological sciences who led the research, said: "Since our own studies had identified Kv1.3's presence in injured blood vessels, which are also often complicated by chronic inflammation, we wanted to see if the same immune system blockers would inhibit neointimal hyperplasia."
Professor Beech said the toxin was "staggeringly potent".
He added: "We're talking about needing very few molecules in order to obtain an effect."
The scientists say it is unlikely margatoxin would be used as a drug to be swallowed, inhaled or injected.
But they add it could potentially be used as a spray-on treatment to the vein itself, once it has been removed and is waiting to be grafted onto the heart.
The research was funded by the British Heart Foundation, the Wellcome Trust and the Medical Research Council.
Professor Peter Weissberg, medical director at the BHF, said: "Although veins make good bypass vessels for patients with coronary artery disease, they're prone to narrow and block off in the years after the operation, so there is a definite need for a treatment that prevents that from happening.
"These results look promising, but we won't know if this approach will benefit patients undergoing bypass surgery until more research is undertaken in patients to establish its long term efficacy and safety.
"This is a good example of a substance that is dangerous in its natural form - a scorpion sting, having potential medicinal benefits if used appropriately."