A modifiedDynatek model MP-1 cardiac pulse duplicatorwas evaluated at the FDA laboratories. It was tested to determine the inherent cycle-to-cycle variability in measuring aortic and ventricular pressure, bulk flow and fluid velocities. Four different prosthetic heart valves were used in the aortic position. Measurements were performed to quantify the percent variability, R, and its standard deviation. The results of this evaluation indicated that the variability, R, decreased for pressure and bulk flow as the number, N, of cycles averaged approached 20. Variability then remained constant at approximately 1%. For the fluid velocity measurements, the variability was much larger and decreased exponentially to 3–15% at N = 100 (depending on valve type, heart rate, and probe/valve position). Preliminary testing of a new duplicator design indicated an improved cycle-to-cycle variability for all measured parameters. In addition, reduced ambient noise and vibration (six fold) were noted, along with a highly stable cycle period. As compared to the Dynatek model MP-1, overall reduction of the variability for the new duplicator varied by a factor ranging from 1 to 16. Average value of improvement was a factor of 4:1, depending on the parameter measured and BPM used.