What is the medical term for the process of measuring heart activity indicated by an ECG?

The medical term for the process of measuring heart activity as indicated by an electrocardiogram is indeed the electrocardiogram itself. An electrocardiogram, often abbreviated as ECG or EKG, is a graphical representation of the electrical activity of the heart over a period of time. It records the timing and strength of these electrical signals, allowing healthcare providers to diagnose various heart conditions, monitor heart health, and determine the heart's rhythm.

The other terms listed refer to different processes: a cardiogram is a more general term that can refer to any graphical representation related to heart activity but is not specifically the measurement process itself. A sonogram is an imaging technique that uses ultrasound to visualize structures within the body, not related to heart activity. A stethogram is not a standard medical term and does not pertain to the electrical activity of the heart.