Research has found that those who have a heart attack in the morning suffer damage up to five times worse than those struck down later in the day, the Daily Mail reported.
Scientists believe it may be due to changes in the body`s blood pressure, hormone levels and metabolism rates that naturally occur when a person wakes up.
The scientists at the National Centre of Cardiovascular Research in Madrid, Spain, studied 811 patients admitted to hospital with heart attacks between 2003 and 2009.
The researchers estimated severity of the attacks by measuring levels of the enzymes creatine kinase and troponin-I, which are higher with the level of damage to the heart muscle, the newspaper said.
It was found that damage to the heart was 21 per cent greater when the attack had occurred between 6 am and midday.
The results of the study, published in the medical journal Heart, also revealed that 269 patients had their heart attack in the 6 am to noon period, followed by 240 patients who had their attack between noon and 6 pm, 161 during the 6 pm to midnight period, and 141 between midnight and 6 am.
Earlier studies had revealed that heart attacks are more likely to happen in the morning than other times of the day, but the new study is the first to show that they are also more severe at this time of day.
Doctors cannot yet explain why heart attacks appear to be more severe in the morning, but believe it may be caused by natural changes that occur in the body over a 24-hour period.