PTCA alters the natural history of coronary artery disease and thus presents a challenge for the cardiologist to detect the variety of changes that may occur. Continuous electrocardiographic monitoring with automatic detection of ST segment changes has proved valuable during the immediate post-PTCA procedure. Radionuclide ventriculography and thallium-201 perfusion scans are most important in providing physiologic evidence of improved functional blood flow, particularly in patients with limited revascularization. Finally, the important unsolved problem with PTCA, that of restenosis, is best detected by repeat noninvasive testing in the first months after successful PTCA.