MODEL RELEASED. Stress test. Nurses monitoring a patient as he performs exercise on a treadmill during a stress test. Electrocardiography (ECG) electrodes on his chest monitor his heart whilst an arm cuff is being used to measure his blood pressure. A stress test assesses fitness by measuring the response of the heart to continuous exercise. It is commonly used to assess recovery following a heart attack. An ECG machine measures the electrical activity of the heart. Each peak on the ECG trace (lower centre) represents a heartbeat and corresponds to the electrical pulses that precede the contraction of the heart muscle.