One person in five is expected to develop heart failure in developed countries, warns the Heart Failure Association (HFA) of the European Society of Cardiology (ESC) while pointing out that public awareness of symptoms is dangerously low.
The risk of death increases when treatment is delayed by few hours after symptoms occur, but many patients remain unaware for hours or even days despite warning signals.
The principal warning includes increasing swelling of the legs, starting with ankles and working upward, and breathlessness while lying flat.
Professor Andrew L Clark, chair of the British Society for Heart Failure (BSH) said: "For patients with untreated heart failure it feels as if every breath in and out is through a narrow straw. Their prognosis is worse than for most forms of cancer. But treatment at least doubles life expectancy and many cases could be prevented if patients knew what do to."
Up to 45% of patients admitted to hospital with heart failure die within a year of admission and the majority die within five years.
Most types of heart failure are preventable with a healthy lifestyle. After the disease has developed, premature deaths could be prevented by recognising the symptoms and seeking immediate medical attention.
Professor Clark said: "Most patients don't get to see a heart failure specialist. This needs to change because when patients are diagnosed quickly and given the best treatment, their chances of survival and a good quality of life dramatically improve."
Countries across Europe hold events to mark Heart Failure Awareness Day on 8, 9 and 10 May.
Heart failure affects 26 million people worldwide and has a striking impact on quality of life. Patients are often scared, anxious and depressed.
The Heart Failure Matters website, provides practical information for patients, families, and caregivers in eight languages.
Patients often delay treatment as they do not relate the symptoms to the heart or believe that it was not severe.
Being physically active, eating a healthy diet and not smoking all help lower the likelihood of obesity, diabetes and high blood pressure, which are also risk factors for heart failure.
Professor Stefan Störk, director of the Comprehensive Heart Failure Centre in Würzburg, Germany, said: "We hope that by targeting healthy people with prevention messages we can stop heart failure from occurring and avert unnecessary deaths and reductions in quality of life."