Many cardiologists rely primarily on catheterization to evaluate, and revascularization to treat, patients with unstable angina. In this era of managed care and cost containment, it is useful to determine whether some patients with unstable angina might benefit sufficiently from noninvasive testing and medical therapies. Several studies provide evidence that myocardial perfusion imaging is valuable for evaluating cardiac risk and thus determining the best candidates for medical treatment. Comparative studies indicate that myocardial perfusion imaging is superior to stress electrocardiography for assessing risk in patients with unstable angina.