Waking up too early and having problems settling back to sleep may have a negative impact on the heart, a study shows.
People who have trouble drifting off to sleep may be at increased risk of heart failure, researchers say.
The study, published in the European Heart Journal, followed more than 50,000 people for 11 years.
Scientists found those who suffered several nights of poor sleep were more likely to develop the condition, in which the heart fails to pump properly.
Experts say further research is needed to see if a lack of sleep causes heart failure or the link is more complex.
Scientists at the Norwegian University of Science and Technology looked at more than 50,000 people aged between 20 and 89. At the beginning of the study, none of them were known to have heart failure.
In this condition the muscles of the heart are often too out of shape to do their job properly - they may be too weak or too stiff to pump blood around the body at the right pressure.
More than 750,000 people in the UK have heart failure and for the majority there is no cure.
People with the disorder may feel increasingly breathless and exhausted.
And as heart failure worsens, it can be difficult to get a full night's rest - but the Norwegian study is one of few to investigate whether poor sleepers without the condition are at risk of getting it in later life.