Tachycardia – Diagnosis and treatment – Mayo Clinic

An electrocardiogram, also called an ECG or EKG, is the most common tool used to diagnose tachycardia. It’s a painless test that detects and records your heart’s electrical activity using small sensors (electrodes) attached to your chest and arms. An ECG records the timing and strength of electrical signals as they travel through your heart.

https://www.mayoclinic.org/diseases-conditions/tachycardia/diagnosis-treatment/drc-20355133