An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler ultrasound.

Echocardiography has become routinely used in the diagnosis, management, and follow-up of patients with any suspected or known heart diseases. It is one of the most widely used diagnostic imaging modalities in cardiology. It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity, location and extent of any tissue damage, and assessment of valves. An echocardiogram can also give physicians other estimates of heart function, such as a calculation of the cardiac output, ejection fraction, and diastolic function (how well the heart relaxes).

Echocardiography is an important tool in assessing wall motion abnormality in patients with suspected cardiac disease. It is a tool which helps in reaching an early diagnosis of myocardial infarction, showing regional wall motion abnormality. Also, it is important in treatment and follow-up in patients with heart failure, by assessing ejection fraction.

Echocardiography can help detect cardiomyopathies, such as hypertrophic cardiomyopathy, dilated cardiomyopathy, and many others. The use of stress echocardiography may also help determine whether any chest pain or associated symptoms are related to heart disease. The biggest advantage of echocardiography is that it is not invasive (does not involve breaking the skin or entering body cavities) and has no known risks or side effects. Not only can an echocardiogram create ultrasound images of heart structures, but it can also produce accurate assessment of the blood flowing through the heart by Doppler echocardiography, using pulsed- or continuous-wave Doppler ultrasound. This allows assessment of both normal and abnormal blood flow through the heart. Color Doppler, as well as spectral Doppler, is used to visualize any abnormal communications between the left and right sides of the heart, any leaking of blood through the valves (valvular regurgitation), and estimate how well the valves open (or do not open in the case of valvular stenosis). The Doppler technique can also be used for tissue motion and velocity measurement, by tissue Doppler echocardiography.

Echocardiography was also the first ultrasound subspecialty to use intravenous contrast. Echocardiography is performed by cardiac sonographers, cardiac physiologists (UK), or physicians trained in echocardiography.

Recognized as the "Father of Echocardiography", the Swedish physician Inge Edler (1911–2001), a graduate of Lund University, was the first of his profession to apply ultrasonic pulse echo imaging in diagnosing cardiac disease, which the acoustical physicist Floyd Firestone had developed to detect defects in metal castings. In fact, Edler in 1953 produced the first echocardiographs using an industrial Firestone-Sperry Ultrasonic Reflectoscope. In developing echocardiography, Edler worked with the physicist Carl Hellmuth Hertz, the son of the Nobel laureate Gustav Hertz and grandnephew of Heinrich Rudolph Hertz.