Intravascular ultrasound imaging is a catheter-based method that has been shown to be better than contrast angiography in the detailed assessment of coronary and peripheral arterial atherosclerotic lesions, arterial dissections and clots, aortic and pulmonary arterial disorders, and the effects and complications of interventional therapy in various vascular beds. Evaluation of refined ultrasound catheters, combined imaging and therapeutic devices, and off-line 3-dimensional reconstruction capabilities indicates that intravascular ultrasound could provide guidance during various catheter-based therapeutic procedures. Early experience with intracardiac echocardiography suggests that this technique could evolve as a clinically useful method with diagnostic, monitoring, and guidance applications. Future directions for further development include designing of miniaturized imaging devices, "look-forward" imaging devices, low frequency devices for whole heart imaging, multifrequency ultrasound catheters and multifunction ultrasound consoles, and approaches to real-time 3-dimensional imaging, on-line tissue characterization, automated acoustic quantification and tissue characterization, the study of myocardial perfusion, and catheter-based acoustic myocardial biopsy. These developments could lead to the conversion of catheterization laboratories into integrated imaging, monitoring, and therapeutic stations. In addition, continuous monitoring of cardiac function could be possible in the critical care unit and in the operating room as well. Ongoing advances in catheter technology and image processing indicate that these concepts are within the realm of becoming reality.