A new drug that helps the heart pump more easily could improve the lives of thousands of people afflicted by debilitating heart failure.
Research shows omecamtiv mecarbil is the first of a new class of drugs, called myosin activators, targeting proteins that make the heart contract.
Rather than forcing the heart to beat more often, the drug causes heart muscles to contract for longer, increasing the volume of blood pumped out with each stroke.
A trial reported in The Lancet medical journal showed that omecamtiv mecarbil significantly improved the heart function of 45 heart failure patients.
Heart failure occurs when the heart becomes too weak to pump sufficient amounts of blood around the body.
The condition can often leave patients breathless and exhausted after just minor levels of activity.
Study leader Professor John Cleland said: "The trial proves that the drug can be given safely to patients suffering from heart failure and shows that, at the correct doses and blood plasma concentrations, it can improve heart function and make the heart contract more effectively." Other heart failure drugs that affect muscle contraction work by boosting levels of calcium inside cells.
This causes the heart to contract at a faster rate, but shortens the time during which blood is pumped out of the heart.
It can also lead to potentially life-threatening side effects such as abnormal heart rhythms and insufficient blood being supplied to the heart muscle.
Currently, omecamtiv mecarbil has to be injected into a vein but scientists are developing a capsule that can be swallowed.
Prof Cleland added: "This initial trial was very promising and further larger-scale studies of the drug are already under way.
"We need to see whether the improvements in cardiac function translate into real benefits for patients, in terms of their symptoms and quality of life, and whether it can impact on mortality (death) and morbidity (illness)."
Omecamtiv mecarbil produced a significant dose-dependent increase across several measures of the heart's pumping function.