Quantitative analysis of biplane ventriculograms, including calculation of the end-systolic pressure/volume ratio, was used to define left ventricular systolic performance in 10 normal subjects, 10 patients with symptomatic subacute (less than 6 months' duration) mitral regurgitation, and 18 patients with symptomatic chronic mitral regurgitation. Left ventricular volume, mass, and systolic function were similar for patients with subacute and with chronic mitral regurgitation, suggesting that some patients with recent-onset nonischemic mitral regurgitation have partial adaptation to chronic valve insufficiency prior to their symptomatic event. Rate of development of left ventricular wall stress in early systole was increased in subacute mitral regurgitation compared with chronic mitral regurgitation and normal subjects. Duration of symptoms did not correlate with degree of ventricular adaptation to mitral regurgitation, and end-systolic indices of left ventricular performance did not predict early postoperative clinical response to valve replacement or repair.