With the ECG app on Apple Watch Series 4, you can take an ECG similar to a single-lead electrocardiogram. The ECG app can record your heartbeat and rhythm using the electrical heart sensor on Apple Watch Series 4 and then check for signs of atrial fibrillation (AFib), a form of irregular rhythm. Allows you to take an ECG similar to a single-lead electrocardiogram Take an ECG at any time, when you’re feeling symptoms such as a rapid or skipped heartbeat, or when you receive an irregular rhythm notification. The ECG app can indicate whether your heart rhythm shows signs of atrial fibrillation—a serious form of irregular heart rhythm—or sinus rhythm, which means your heart is beating in a normal pattern. Saves ECG waveform, classification and any noted symptoms in a PDF on the Health app on iPhone to share with your doctor.