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Pressure examination, hammer examination, ultrasonography are some common examples of non-invasive methods, and there are many non-invasive methods used in HF. Each method will be briefly mentioned in this section.

Electrocardiography is one of the non-invasive methods in HF. It monitors heart rhythm changes by recording the heart's electrical activity and, thus, determines whether a heart attack has occurred from abnormalities in rhythm. Electrocardiography and blood tests are the most common methods used in HF diagnosis and the aim of electrocardiography is to determine the complex factors underlying HF [5].

Sometimes, the heart’s activity is recorded throughout the day, not just for a short time. This process is known as Holter monitoring. The method aims to determine how the heart responds during daily activities and the average heart rhythm. Holter monitoring not only detects abnormalities in the heart, but can also help doctors treat them.

Chest x-ray also provides a non-invasive method for diagnosing heart diseases, by taking a picture of the heart, lungs, and rib cage. With the radiological imaging performed, it can be seen if the heart is enlarged after a heart attack or fluid accumulation in the lungs. Systolic and diastolic dysfunction of the heart can be discovered through electrocardiography and chest x-ray [6].

Echocardiography has been used for many years to characterize HF [7]. It uses high frequency sound waves (ultrasound) to produce images of heart size, movement, and structure. The printout of the test gives information about heart health and helps to gather information about heart arrhythmias. Echocardiography outputs have been used with both machine learning algorithms and deep learning algorithms [8].

Computed imaging (tomography) is used to detect other diseases as well as in HF. It creates three-dimensional (3D) images that can show the obstructions in our main vessels with the help of a computer system. Through computed tomography, testing can be performed, especially for aortic disease.

The exercise test works with skin-attached electrodes and a monitor recording a person’s heart function while walking on a treadmill. Many aspects of heart function can be checked, including heart rate, breathing, blood pressure, ECG, and how tired someone is while exercising. This test is particularly helpful in diagnosing CAD and is also used to predict heart attack risk. It helps diagnose the possible cause of symptoms such as chest pain (angina).

The last procedure on this subject is known as the thallium stress test. The thallium test is similar to a routine exercise stress test. The difference is that the radioactive thallium material injected into the patient’s blood is photographed by special gamma ray cameras when the patient is at the maximum exercise level. Thus, the extent of coronary artery occlusion can be determined and the extent of damage from heart attack can be determined [9].