The term echocardiography refers to the evaluation of cardiac structure and function with images and recordings produced by ultrasound. In the past three decades it has rapidly become a fundamental component of the cardiac evaluation. Currently, echocardiography ("echo") provides essential (and sometimes unexpected) clinical information and has become the second most frequently performed diagnostic procedure after electrocardiography.¹ What began as a one-dimensional (1D) method performed from the precordial area to assess cardiac anatomy has evolved into a two-dimensional (2D) modality performed from either the thorax or from within the esophagus, capable of also delineating flow and deriving hemodynamic data.² Newly evolving technical developments likely will extend the capacity of ultrasound to routine 3D visualization³ as well as to the assessment, in conjunction with contrast agents,⁴ of myocardial perfusion.

The development of echocardiography is usually credited to Elder and Hertz in 1954.⁵ Primitive cross-sectional images of the excised human heart were produced in 1957⁶; however, for nearly two additional decades, clinical echocardiography consisted primarily of 1D time-motion (M-mode) recordings, as popularized by Feigenbaum.⁷ In the mid-1970s, Bom and associates developed a multielement linear-array scanner that could produce spatially correct images of the beating heart.⁸ 2D images of superior quality were soon achieved by mechanical sector scanners⁹,¹⁰ and ultimately by phased-array instruments as developed by Thurston and Von Ramm, which are the present-day standard.¹¹ In the past several years, 3D instruments capable of real-time volumetric imaging have been developed.¹² Miniaturization of ultrasound transducers has also led to their incorporation into gastroscopes and cardiac catheters to achieve transesophageal and intravascular images.¹³,¹⁴

Although efforts to use the Doppler principle to measure flow velocity by ultrasound were begun in the early 1970s by Baker et al.,¹⁵ clinical application of this technique did not thrive until the work of Hatle in the early 1980s.¹⁶,¹⁷ Pulsed and continuous-wave Doppler recordings soon were expanded to full 2D color-flow imaging. Most recently, Doppler velocity recordings have been obtained from myocardium itself, enabling measurement of tissue velocities and regional strain.