Final answer:
Heart failure is most definitively diagnosed with an echocardiogram, an ultrasound imaging test that provides detailed information on the heart's structure and function.
Step-by-step explanation:
The diagnosis of heart failure is often confirmed through a variety of diagnostic tests, but the most definitive among them is the echocardiogram (ECHO). An echocardiogram is an ultrasound imaging test that provides a detailed view of the heart's structure and function, including how well the heart valves and muscles are working. Although other tests such as a chest X-ray can show whether the heart is enlarged, and an electrocardiogram (ECG or EKG) can measure the heart's electrical activity, the echocardiogram is superior in evaluating the pumping function of the heart and identifying heart failure.