The role of short-lived gaseous radiotracers in myocardial function studies is reviewed. The evaluation of shunts and ejection fractions characterizing individual chambers is best performed with tracers restricted to those chambers. Classic examples include the C15 O2 inhalation radiocardiogram for probing the left-heart performance, with the right heart illuminated by intravenous 133Xe in saline. A more elegant utilization of rapid physical decay to unravel flow patterns is seen in the use of 81m Kr. Krypton-81m is swept from its parent 81Rb, either confined to an extracorporeal generator or an in vivo rubidium distribution. The steady-state images that result contain a wealth of dynamic information distilled into its most lucid format.