A holter monitor is a portable EKG that monitors the electrical activity of a freely moving person's heart generally for one to two days, 24 ours a day. It is most often used when the doctor suspects an abnormal heart rhythm or ischemia (not enough blood flow to the heart muscle).
It is a painless test; electrodes from the monitor are taped to the skin. Once the monitor is in place, you can go home and perform all of your normal activities (except showering). You will be asked to keep a diary of your activities and any symptoms you experience and when they occur.
An echocardiogram is a test that uses ultrasound to evaluate your heart muscle, heart valves, and risk for heart disease.
The exercise stress test -- also called a stress test, is used to test for heart disease. Stress tests are tests performed by a doctor and/or trained technician to determine the amount of stress that your heart can manage before developing either an abnormal rhythm or evidence of ischemia (not enough blood flow to the heart muscle). It is used to provide information about how the heart responds to exertion. It usually involves walking on a treadmill at increasing levels of difficulty, while your electrocardiogram, heart rate, and blood pressure are monitored.