Radioisotopic cardiac investigation techniques still have a limited role in intensive care units, mainly due to cumbersome traditional equipment, even if in some cases favourable local circumstances exist, such as the proximity of a nuclear medicine unit or the availability of a mobile gamma camera. Nevertheless, nuclear techniques show a number of interesting features, mainly related to the fact that measurements of cardiac chamber volumes and of their variations can be directly derived from activity counts, without any geometrical hypothesis as it is necessary for other methods such as contrast angiography or echocardiography. The whole cardiac cycle (its systolic part as well as its diastolic part) can therefore be evaluated. In addition, since the blood pool labelling remains stable for a long period after a single tracer injection, continuous monitoring of critically ill patients becomes possible. In this case it is no longer the gamma camera imaging system which may be used but rather a very sensitive miniature detector associated with a computerized data acquisition system, allowing beat-by-beat assessment of cardiac activity. The development of this device raises specific problems related to detection geometry, elimination of extracardiac background and stability of the probe positioning on the patient's thorax, but it is clear that such a system merits its place in an intensive care unit in the near future.