Over the 40 years since its discovery, many studies have focused on understanding the role of troponin as a myofilament based molecular switch in regulating the Ca2+-dependent activation of striated muscle contraction. Recently, studies have explored the role of cardiac troponin as a target for cardiotonic agents. These drugs are clinically useful for treating heart failure, a condition in which the heart is no longer able to pump enough blood to other organs. These agents act via a mechanism that modulates the Ca2+-sensitivity of troponin; such a mode of action is therapeutically desirable because intracellular Ca2+ concentration is not perturbed, preserving the regulation of other Ca2+-based signaling pathways. This review describes molecular details of the interaction of cardiac troponin with a variety of cardiotonic drugs. We present recent structural work that has identified the docking sites of several cardiotonic drugs in the troponin C-troponin I interface and discuss their relevance in the design of troponin based drugs for the treatment of heart disease. (c) 2007 Elsevier Inc. All rights reserved.