MODEL RELEASED. ECG test. Doctor examining a young woman while she undergoes an electrocardiogram (ECG) test. She is wearing an oxygen mask. The electrodes attached to the woman's chest measure the electrical activity of her heart. An ECG can be used to diagnose a range of heart complaints, such as arrhythmia, coronary artery disease and cardiac asthma. Oxygen therapy supplies oxygen- enriched air to patients who have symptoms of hypoxia (inadequate oxygen in the body tissues). It is used to treat lung and breathing disorders.