Nine in 10 people with coronary heart disease in the UK are living with at least one other long-term condition, such as stroke, dementia and high blood pressure, figures show.
The analysis by the British Heart Foundation (BHF) shows six in 10 heart patients have at least three other long-term conditions.
Previous studies have shown that living with multiple conditions significantly increases the risk of early death.
The BHF said the growing number of people living with inter-related health conditions represents a grave challenge for the health system, which is focused on treating individual illnesses.
The analysis reveals the most common comorbidity for people living with coronary heart disease is high blood pressure, which affects over half of patients.
This is followed by 26% of heart patients who have diabetes, 14% who have had a stroke, 13% who are living with heart failure, and 5% who have dementia.
People with coronary heart disease, including those who have suffered a heart attack, are more than twice as likely to suffer a stroke or develop vascular dementia.
There was a fourfold increase, from 6.4% to 24.3%, in the number of patients with heart and circulatory diseases living with five or more additional illnesses from 2000 to 2014.
Simon Gillespie, chief executive of the BHF, said the figures point towards an emerging and very urgent challenge.
“For example, increasing numbers of people are surviving heart attacks, but are going on to suffer strokes or live with additional conditions like vascular dementia. These conditions limit people’s quality of life, increase their risk of dying and will place increasing pressure on the health and care system across the UK,” he warned.