There are a number of tests used to help diagnose heart failure.
Blood tests
A Natriuretic peptide test is a useful blood test to help determine if someone has heart failure. If the test is normal it is highly unlikely heart failure is present and other causes for symptoms must be investigated. It is a simple blood test and the results can usually be available in a few days.
Echocardiogram
An echocardiogram is also called a heart ultrasound test and is used to directly visualise the heart muscle and heart valves. It involves using a probe and some gel on the chest wall to view the heart on a screen. It is completely painless and helps determine how efficiently the heart is working. It can also provide information on the heart valves. The results are available immediately and this test is very useful to provide a quick diagnosis. It can also be useful in other conditions such as high blood pressure. The test is also useful if you have a heart murmur.
Cardiac MRI
This is a specialised scan of the heart using a magnetic resonance scanner. It provides greater detail about the function of the heart and the valves as well as additional information about the degree of scarring in the heart. It does involve the patient lying in an enclosed space for 45 minutes to 1 hour and holding their breath periodically.