In 19 subjects with various degrees af left ventricular heart failure, regular(R), extrasystolic (ES) and post-extrasystolic (PES) ejection fractions(EF) were determined using an nuclear stethoscope. As compared to EF(R). EF(PES) did not change significantly in patients with the first degree heart failure, but it increased significantly in patients with the second degree failure ((EF(R) = 38.4 +- 7.7 (x +- SD). EF(PES) = 43.7 +-10.8 (x +- SD), p 0.01)), and to an even greater extent in subjects with the third degree heart failure ((EF(R) = 22.8 +- 6.2 (x +- SD), EF(PES) =32.3 +- 9.9 (x +- SD), p 0.01)). A comparison of EF(PES) and EF(R) revealed no significant difference between the patients with the first degree failure and those with the second degree heart failure, yet a significant difference was observed between the group with the first degree and that with the third degree heart failure (( 89.8 +- 13.6 (x +- SD). 142.7 +- 29.8 (x +- SD), p