Nuclear stress test is an imaging method that uses radioactive material to show how well blood flows into the heart muscle, both at rest and during activity. A stress echocardiography, also called an echocardiography stress test or stress echo, is a procedure that determines how well your heart and blood vessels are working. During a stress echocardiography, you'll exercise on a treadmill or stationary bike while your doctor monitors your blood pressure and heart rhythm.