An intra-aortic compression chamber system (CCS) was utilized in 19 anaesthetized dogs and in seven patients. The CCS consisted of an intra-aortic balloon in the thoracic aorta, an external rigid wall air chamber, and a catheter connecting the other two parts. The CCS, inflated for 2-3 min to a pressure between the systolic and diastolic arterial pressures, caused changes in the following measurements (compared with those immediately before inflation, and after deflation to atmospheric pressure): a significant (P less than 0.001) increase in cardiac output (7.8 +/- 18.8% means S.D.), aortic compliance (12.8 +/- 29.6%), aortic resistance (20.1 +/- 32.7%), cardiac power (or minute work, + 36.7 +/- 44.6%), coronary sinus outflow (+ 23.6 +/- 43.6%) and aortic backflow (+ 28.0 +/- 36.4%); the left ventricular end-diastolic pressure did not change significantly. During a 5-90 min utilization in seven patients with cardiogenic shock, the cardiac output was increased by 4.1 +/- 42.4% (lower than when intra-aortic balloon pumping was applied). It is concluded that the simple device described may be useful in clinical cardiogenic shock, especially when an intra-aortic balloon pump is not available or a portable device is desirable.