The time of day a person suffers a heart attack could have major implications for the patient, according to new research.
Scientists from the Minneapolis Heart Institute Foundation found that heart attacks suffered between 01:00 and 05:00 tend to be more severe than those that occur at other times of the day.
"It is important to understand that the heart's ability to protect itself against more severe damage varies over a 24-hour cycle," said the study's author Jay Traverse, a cardiologist at the Institute.
He believes the findings may help drug manufacturers develop medicines which can help more effectively protect a person's heart and cardiac system.
According to the British Heart Foundation, most heart attacks are caused by the arteries around the heart becoming blocked with fatty material, which subsequently deprives the cardiac muscle in the heart of oxygen.
The charity advises anyone aged over 40 to ask their doctor for a health check to assess their individual risks.