Heart fitness test. Electrocardiogram (ECG) device showing the output from electrodes monitoring the heartbeat of a patient taking a heart fitness test. The main screen shows the electrical trace of the heartbeat. The diagram at left shows where the electrodes are placed on the patient. The ECG output will be recorded as the patient exercises. Changes in the measurements during exercise allow an assessment of the patient's cardiovascular fitness. Disorders like arrhythmia (irregular heartbeat), and some forms of coronary artery disease, can be diagnosed from the test.