Scientists claim the breakthrough discovery can help treat heart-attack victims to cut their risk of developing heart failure.
The condition affects more than 500,000 people across the UK and means their heart can no longer pump blood around their body efficiently, leading to shortness of breath, a build-up of fluid and fatigue.
Every year, hospitals in the UK record a total of 188,000 heart attacks - about one every three minutes. Seven out of 10 people now survive a heart attack but many are left with heart failure.
Bleeding, or bruising in the heart, affects more than 40% of heart-attack patients and researchers have discovered this injury is associated with a six-times higher risk of heart failure or death in the months following a heart attack.
The study also identified when treatments could be brought in to stop the bleeding and cut the risk of heart failure.
Following a heart attack, an MRI scan can be used to monitor bleeding from the heart.
The bleeding happens in two phases, 12 hours after and then 2-3 days later. This provides a window of opportunity to introduce treatments to stop the second phase, which could reduce of prevent later heart failure.
Researchers validated a test for use at the time of heart-attack treatment to rule in or rule out heart muscle bleeding, and the likelihood of survival free of heart failure, paving the way for new treatments.
Professor Colin Berry, from the University of Glasgow, who led the study said: “This research has provided us with a new understanding of heart muscle injury and how it develops.
“We can now focus our research on developing new treatments to reduce the level of this injury following a heart attack.
“The study has also presented a new way of identifying those at a higher risk of heart failure before the condition develops.
“This knowledge can be used to identify those most in need of interventions and monitoring earlier.”
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, which funded the research, said: “Heart failure is an incurable condition which is associated with a reduced quality of life and a lower life expectancy.
“This exciting research has found a new characteristic related to heart attacks which could be used to treat people following a heart attack, to cut their risk of developing heart failure.”