The most serious heart attacks happen in the morning, research has shown. Between 6am and noon, a heart attack is likely to affect 20 per cent more of the organ than if it happens at another time, according to doctors in Spain.

Heart attacks are more common in the morning as people wake up, as a result of physiological influences controlled by the 24-hour body clock. Now the study has shown that as well as being more common, they are more serious. The researchers, who analysed data on over 800 patients, say in the journal Heart that those who had a morning heart attack had 21 per cent more enzymes released, indicating greater damage.

The bigger the area of the heart affected, the more serious it is and the more protracted the recovery. Heart muscle dies when its blood supply is blocked by a clot in a coronary artery and the damaged organ is afterwards less able to pump blood round the body.

Judy O'Sullivan, senior cardiac nurse at the British Heart Foundation, said: "Regardless of the time of day, the quicker someone having a heart attack is treated, the less the damage they will have, which is why it is essential that anyone who experiences heart attack symptoms should call 999 immediately."