Fiber optic techniques lend themselves to continuous physiologic monitoring of an array of hemodynamic and other key variables in the critically ill. The factor limiting clinical application has been the rapid clot formation at the sensing tip. By developing a side-viewing fiber optic probe, clotting was prevented during prolonged periods of intravascular monitoring. The catheter has been adapted to monitor multiple physiologic changes, including cardiac output, oxygen saturation, dye clearance, intravascular pressure, and heart rhythm. The procedure has been well tolerated and has required but a minimum of bedside instrumentation. These preliminary studies were conducted in patients with acute myocardial infarction.