Dr. Markowitz's research concerns indentifying the bases of arrhythmias in humans, including atrial and ventricular tachycardias. Mechanisms and Properties of Atrial Tachycardias This research concerns the mechanisms and properties of focal and macroreentrant atrial tachycardias. We have described the origin of atrial tachycardias in normal, myopathic, and post-surgical hearts, and we have identified the electropharmacological profiles of these diverse atrial arrhythmias. Advanced Imaging in Patients with Idiopathic Ventricular Tachycardia This ongoing project utilizes new cardiac imaging modalities, such as MRI, 3-dimensional echocardiography, and PET scanning, to distinguish idiopathic ventricular tachycardia from right ventricular cardiomyopathies and to better understand the mechanism of outflow tract tachycardias. Atrioventricular Nodal Physiology in Humans Our laboratory investigates AV nodal physiology, with emphasis on understanding the basis for dual pathway physiology. We have presented evidence for the existence of separate anterior and posterior inputs to the AV node, with different electrophysiological properties.