What type of tests does an Electrocardiogram (EKG) measure?

An Electrocardiogram (EKG or ECG) measures heart function by recording the electrical activity of the heart over a period of time. This test shows how well the heart is functioning and can help identify various cardiac conditions such as arrhythmias, heart attacks, and other heart diseases. The electrical impulses that trigger heartbeats are captured in the form of waves on a graph, allowing healthcare professionals to assess the heart's rhythm and overall health.

In contrast, the other options focus on different bodily systems and processes. For example, brain activity is typically measured using electroencephalograms (EEGs), lung capacity is assessed through pulmonary function tests, and muscle response is often evaluated with electromyography (EMG). Thus, the EKG is specifically designed to provide insights into cardiac health, making "heart function" the accurate choice for what it measures.