Migrating of electrical impulses around the heart can be traced by an electrocardiograph. ECG machine measures electrical activity of the heart in the different phases of the cardiac cycle and traces these patterns as waves in a graphic paper known as an electrocardiogram (ECG, sometimes known as EKG).
Each wave exactly corresponds to a specific part of cardiac cycle. By interpreting ECG trace, conduction abnormalities, rhythm disturbances, electrolyte imbalances, drug administration, chambers enlargement can be detected.