Contrast-enhanced ultrasound imaging is a radiation-free clinical diagnostic tool that uses biocompatible contrast agents to enhance ultrasound signal, in order to improve image clarity and diagnostic performance. Ultrasound enhancing agents (UEA), which are usually gas microbubbles, are administered intravenously either by bolus injection or continuous infusion. UEA increase the accuracy and reliability of echocardiography, leading to changes in treatment, improving patient outcomes and lowering overall health care costs. In this review we describe: (1) the current clinical applications of ultrasound enhancing agents in echocardiography, with a brief review of the evidence underlying each of these applications; (2) emerging diagnostic and therapeutic applications of microbubble enhanced echocardiography (MEE), which rely either on the specific properties and composition of ultrasound enhancing agents or on the technical advances of clinical ultrasound systems; and (3) safety of MEE.