This video is an echocardiogram (ultrasound) of a human heart during actual resuscitation. All four chambers of the heart are visible. When chest compressions are stopped briefly, blood stagnates and appears as "smoke" in the chambers.
When compressions resume, the right atrium and ventricles (seen on the left of the screen) clear quickly since the sternum directly squeezes blood out into the pulmonary circuit. The left atrium and ventricles (seen on the right side of the screen) take seven or eight beats before they clear because blood has to make its way through the pulmonary circuit before significant momentum is created to provide substantial pressure and flow into the aorta.
The importance of this video is that is shows how vital it is to NOT interrupt chest compressions unnecessarily because there is no oxygen delivery to the body when compressions are stopped and it takes 5-10 seconds after compressions are resumed for significant pressure and flow to resume.
Joseph P. Ornato, MD, FACP, FACC, FACEP, is professor and chair of the Department of Emergency Medicine at Virginia Commonwealth University/Medical College of Virginia in Richmond. He is also medical director of the Richmond Ambulance Authority, the prehospital paramedic system serving the city of Richmond.