Obese and very obese patients have a lesser chance of dying after treatment for heart attacks than normal-weight patients.
The researchers measured the body mass index (BMI) of 1,676 patients who suffered a cardiac incident.
It was found that 9.9 per cent of those with a normal BMI and 7.7 per cent of the overweight patients died within three years of receiving treatment.
Dr Heinz Buetter, who led the study, said: "Although there is no doubt that people who are overweight, obese and very obese have a higher risk of developing diabetes, hypertension and coronary artery disease, the evidence from our study shows once a coronary event has occurred and been optimally treated, obese patients switch to a more favourable prognosis."
The results have been explained in part since obese patients suffering heart attacks tended to be younger and less likely to have suffered a prior heart attack.
However, the researchers say that their findings do contrast with prevention studies that implicate BMI as a strong risk factor in relation to mortality.