The development of newer electrophysiological mapping and ablation procedures for the treatment of complex arrhythmias has led to the advent of a new application of echocardiography. The introduction of intracardiac echocardiography to the electrophysiology laboratory has created a marriage between imaging and intervention that is generating new insights for the echocardiographer and added safety for the electrophysiologist. This review will discuss the history, principles, approaches, and potential future applications of intracardiac echocardiography.