In this paper the cardiac actions of adenosine, as well as its therapeutic and diagnostic applications are reviewed. Adenosine has been demonstrated to be useful in the assessment of coronary artery disease in conjunction with perfusion SPECT scintigraphy, PET imaging and two-dimensional echocardiography. The reported sensitivities and specificities of adenosine in these settings are high and similar to those of imaging after exercise or dipyridamole induced coronary hyperemia. Minor side effects are commonly associated with adenosine infusion, however they are transient, generally well tolerated, and rarely require test termination or the administration of aminophylline. Adenosine has proven very useful in the noninvasive diagnosis of Wolff-Parkinson-White syndrome and in the localization of the ventricular insertion of the accessory pathway. As a provocative test, adenosine 12.0 mg rapid bolus has a sensitivity and specificity of 100% for identifying anterograde atrioventricular accessory pathway conduction. The use of adenosine is particularly well suited to the technique of echocardiographic phase analysis and cine-loop inspection as image acquisition is rapid and may be obtained on-line. Although the only approved therapeutic use of adenosine is in the emergency treatment of paroxysmal supraventricular tachycardia, several other clinical applications are suggested by the agents specific cardiovascular and electrophysiologic properties. These include 1. post-thrombolytic therapy to reduce reperfusion injury, 2. as an afterload reduction agent in malignant hypertension and congestive heart failure, 3. to produce controlled hypotension intraoperatively during vascular procedures, and 4. to terminate catecholamine and exercise mediated ventricular tachycardia. Furthermore, the technique of adenosine echocardiographic phase analysis offers the potential for precise subsegmental localization of accessory pathways which has never been achieved by any noninvasive technique, and adenosine augmentation of preexcitation obviates the need for invasive cardiac pacing. Future applications of adenosine scintigraphic and echocardiographic methods will undoubtedly involve newer imaging modalities, such as multiplanar transesophageal and magnetic resonance imaging, which may improve our current abilities to localize accessory pathways and noninvasively diagnose coronary artery disease.