Around half of people with heart and circulatory diseases have found it harder to get medical treatment since the COVID-19 pandemic began, a survey suggested.
In addition, almost a third had found it harder to get the medicines they needed for conditions such as congenital heart disease, heart rhythm problems, previous heart attack or stroke.
The findings were based on a poll by YouGov of 1409 adults with known heart and circulatory conditions.
The British Heart Foundation (BHF), which commissioned the study, said that difficulties in accessing treatment and care could have a damaging impact on people's health, and even result in an increase in deaths.
It could also lead to increased pressure on NHS services if heart and circulatory patients became sicker while awaiting hospital investigations and treatment.
The survey found that, of the people who found it more difficult to access medical treatment from a healthcare professional during the COVID-19 pandemic:
41% said they'd had a planned test, surgery, or procedure postponed or cancelled
48% said a lack of available face-to-face appointments was a reason for this
42% said they did not want to put extra pressure on the health service
The BHF said it was calling on the Government and the NHS to urgently address the immediate needs of heart and circulatory patients who have had care postponed during the coronavirus pandemic.
It said this could be accomplished by increasing the number of heart procedures, surgeries, and tests carried out, such as procedures for pacemakers and stents, as well as heart imaging tests.
It also wanted to see NHS support systems being restored for people with conditions such as heart failure, to keep people out of hospital.
Dr Sonya Babu-Narayan, BHF associate medical director, said: "While doing all we can to fight the virus, we must continue to provide care for people with heart and circulatory conditions in a safe way.
"At the very least, around 28,000 planned inpatient heart procedures have been deferred in response to the COVID-19 outbreak in England alone. This backlog will only get larger and the patients in need of treatment could get sicker as their care is delayed further. If hospital investigations and procedures are delayed too long, it can result in preventable permanent long-term complications, such as heart failure.
"In addition, non-hospital-based health services must not be forgotten, as these enable people with heart and circulatory diseases to stay well and out of hospital."
Sarah Miles, 45, a former nurse and mother of two from Somerset, had a heart attack and cardiac arrest at the age of 38, which led to heart failure. She was advised to shield because she was considered by her doctors to be at extremely high risk of developing complications from the virus.
She told the BHF: "I've had a series of delayed or cancelled appointments, and I’m worried this could have a serious impact on my physical and mental health.
"A planned assessment to consider whether I am suitable for and need a potentially life saving heart transplant was cancelled.
"As well as heart failure, I also have diabetes, and my latest diabetes review was postponed. Getting medication has also been an issue for me.
"The trouble I’ve had in accessing treatment and care has caused me great anxiety because I worry about the potential long-term impact on my health. It will be such a relief when services start to go back to normal, whenever possible."
The survey followed a warning from Cancer Research UK that disruption to the NHS during the pandemic had led to around 2.4 million people in the UK waiting for cancer screening, further tests, or cancer treatment, and tens of thousands of cases left undiagnosed.
Macmillan Cancer Support said it wanted to ensure that cancer did not become "the forgotten 'C'".