The study was funded by the Scottish Government's Chief Scientist Office and was published in the journal BMC Medicine.

As per the study, the risk of death 30 days after a heart attack for people with schizophrenia was doubled when compared with those without the condition.

There was no evidence of any improvement across the 24 year period up to 2014 examined in the study.

Researchers said that the findings highlight the chronic health inequalities faced by people with serious mental illness and are calling for disparities to be urgently addressed.

Experts at the University of Edinburgh examined anonymous hospital data for more than 235,000 people admitted for heart attack in Scotland from 1991 to 2014.

They compared the risks of death and further heart attack and stroke among heart attack patients with schizophrenia, major depression, or bipolar disorder to patients without a history of mental illness.

The research team found that people with one of these three conditions were more likely to die within 30 days, one year, and five years - and to have another heart attack or stroke - compared with those without mental ill-health.

After 30 days, patients with schizophrenia were twice as likely to have died, and patients with bipolar disorder or major depression had a 30-50 per cent increased risk of death.

People with severe mental illness were also less likely to receive revascularisation - an operation to restore blood flow - which researchers said may indicate differences in care.

Researchers said the findings may be due to a number of reasons including poor general health, social exclusion, and possible differences in longer-term treatment.

The research team advised that people with mental health conditions should continue to seek advice from their medical team if they have any concerns about their health.

Dr Caroline Jackson, the lead researcher at the University of Edinburgh's Usher Institute, said, "This study highlights marked and persistent mental health inequalities in heart attack outcomes in Scotland. The underlying reason is likely to be multifactorial and complex and remains poorly understood."

"We need to know how comorbidities and lifestyle factors contribute to these disparities. We also need detailed investigation of the entire patient journey, from heart attack onset to rehabilitation among people with severe mental illness, to identify any areas of weakness in clinical care," Dr Jackson added.

Frances Simpson, CEO of Support in Mind Scotland, who was not involved in this study, said, "Parity of esteem between physical and mental health is imperative if we are to reduce premature deaths. We need to raise awareness amongst physical health professionals of symptoms that can be masked by the side effects of psychiatric medication, and accept that people with mental illness may need more time and support to accept medical procedures."

"Poor physical health is often accepted as an inevitable outcome of living with schizophrenia or bipolar illness, but we believe that everyone has a right to the best possible health care," Simpson concluded.