A feature of the human heart first sketched 500 years ago by Leonardo da Vinci is finally understood by scientists.
Leonardo sketched the mesh-like structure trabeculae inside the organ and speculated they warmed the blood but was unable to prove this.
Modern scientists had, until now, also been unable to ascertain their function.
But a piece of research has now found this network of fibres allows blood to flow through the heart more efficiently.
People with more branches on these muscle fibres also appear to be at a lower risk of heart failure, the study found.
The findings could in future lead to better treatment for the condition, which causes exhaustion and breathlessness, researchers believe.
This is a condition affecting around 920,000 people in the UK and a leading cause of deaths among Britons.
A team of researchers, including Imperial College London, used artificial intelligence to analyse 25,000 magnetic resonance imaging (MRI) scans of the heart.
‘Our work significantly advanced our understanding of the importance of myocardial trabeculae,’ explains Hannah Meyer, a Cold Spring Harbor Laboratory Fellow.
The results also suggest having less complex muscle fibres under the surface of the heart’s chambers can put someone at greater risk of heart failure.
It is possible to increase the number of branches on trabeculae by taking exercise, which makes muscles and fibres in the heart stronger and complex.
Dr Declan O’Regan, who led the study from the Medical Research Council (MRC) London Institute of Medical Sciences, based at Imperial, said: ‘Leonardo da Vinci sketched these intricate muscles inside the heart half a millennium ago, and it is only now that we are beginning to understand how important they are to human health.’
Researchers also discovered six regions in human DNA which affect how the fractal patterns in the muscle fibres develop.
They further found that two of these genes also regulate branching of nerve cells, suggesting a similar mechanism at work in the developing brain as well as the heart.
The scans revealed the intricate structure of the muscle fibres and allowed researchers to investigate their role in heart function.
Dr O’Regan said: ‘This network of muscles lies between fast-flowing blood inside the heart and the contracting heart muscle.
‘We also found that these fibres influence how fast electrical impulses travel through the heart – so they may be important for more than one aspect of how the heart works.’
The findings are published in the journal Nature.