The main thing your doctor wants to see is the electrical activity in your heart. She’ll probably do some tests to see what’s going on.

Tests for atrial fibrillation include:

Blood tests to check your thyroid, liver, and kidneys

Electrocardiogram (EKG) to record how fast your heart is beating and the timing of electrical signals that pass through it. A nurse or technician will place about 12 small, sticky sensors on your chest. Wires connect them to a machine that takes the measurements.

Chest X-ray to make sure lung disease isn’t the cause of your problems

Echocardiogram, which uses sound waves to make a video of your heart working

CT scans, special X-rays that make a 3D picture of your heart MRI, which uses magnets and radio waves to create snapshots and videos of your heart

Exercise stress test to see how your heart works when you’re active. You might walk on a treadmill or ride a stationary bike while wearing sensors connected to an EKG machine.