For nearly 20 years, injections of intravenous contrast agents have been employed to enhance echocardiographic assessment of cardiac anatomy and function.' Used initially to assist early investigators in identifying the structural features of M-mode contrast echocardiography has been extended to a broad range of applications including the demonstration of intracadiac shunt^,^ diagnosis of tricuspid insufficiency as well as evaluation of its severity,6 and anatomical definition of complex structural heart d i ~e a s e . ~ This technique has also enhanced our understanding of normal physiologic processes by revealing the magnitude and direction of intracardiac flows in patients with a patent foramen ovale* and by permitting estimation of cardiac o ~t p u t . ~
In recent years, Doppler echocardiography and high-resolution two-dimensional imaging have replaced many of the applications of intravenous contrast. Nonetheless, contrast echocardiography continues to be useful in a number of circumstances, including the diagnosis of atrial septal defects, assessment of the direction of low-velocity intracardiac shunting, diagnosis of ventricular septal defect resulting from myocardial infarction, identification of abnormal systemic veins, and delineation of anatomical defects in a subset of patients with complex congenital cardiac disease.
Numerous agents have been proposed for the production of intravascular ultrasonic contrast including saline," indocyanine green," hydro-From the