Evaluation of the heart while it is working harder and beating faster than usual, such as during exercise. Stress testing may help uncover heart problems that may not be evident while the body is at rest. During the most commonly used type of stress testing, called exercise stress testing, the person walks or runs on a treadmill or rides a stationary bicycle while various tests are performed. These may include blood pressure testing, electrocardiography (monitoring of the electrical activity of the heart muscle to detect irregular heart beats), and nuclear imaging (using a harmless radioactive substance injected into the bloodstream to produce images of the inner structure of the heart). In a person who may not be able to tolerate exercise, a pharmacological stress test (also known as a chemical stress test) may be used. The person is given a drug, such as dipyridamole (brand name Persantine) or dobutamine (Dobutrex), that increases blood flow to the heart to simulate exercise. The pharmacological stress test may be used in conjunction with electrocardiography, echocardiography, or nuclear imaging.