Algorithms have been developed for the automatic determination of end-diastolic (EDP) and systolic (SYSP) pressures from left ventricular (LV) pressure waveforms acquired during cardiac catheterization. The algorithms were developed using two independent sets of LV waveforms designated the training set and the test set. Eight cardiologists independently analyzed each waveform in both the test and training sets. The training set data was repetitively processed by the computer. In each iteration algorithm parameters were adjusted to reduce the error between the computer analysis and the average of the eight physicians. When this process was completed, the validity of the final algorithms was verified by comparing computer and physician analysis of the test set data in a prospective manner. Interphysician variability (average standard deviation for all beats analyzed) for the test set was 1.47 mm Hg for EDP and 1.87 mm Hg for SYSP. The mean difference between automatically determined pressures and the average results of the eight physicians was 0.98 mm Hg for EDP and 0.97 mm Hg for SYSP. Automatically determined pressures were more accurate than pressures measured by all but one physician for SYSP and two physicians for EDP. The algorithm has been incorporated into a catheterization laboratory system and is in routine clinical use.