Electrocardiography / Humans / Beta decay / Female / Male / Heart rate / Aged / Middle Aged / Thallium / Cardiovascular system / Electrocardiogram / Coronary Angiography / Adult / Coronary heart disease / Public health systems and services research / Radioisotopes / *Physical Exertion / Exercise Test / The American / Heart rate / Aged / Middle Aged / Thallium / Cardiovascular system / Electrocardiogram / Coronary Angiography / Adult / Coronary heart disease / Public health systems and services research / Radioisotopes / *Physical Exertion / Exercise Test / The American