A) Left ventricular (LV) diameter in diastole (dia) is increased in E2- but decreased in M1/2-KO mice vs. control (E2, M1/2, CTRL). B, C) LV diameter in systole (sys) is increased and ejection fraction (EF) is reduced only in the E2-KO. D) E to A ratio is increased in E2-KO only. E) Doppler traces with similar E and A waves in control and M1/2 vs. E2 with a blunted A wave. F, G) Total passive stress of multicellular myocyte preparations is decreased in E2-KO, but not in M1/2-KO. The individual contribution of titin vs. collagen based stress is provided in Supplemental Figure 4B, C. Data in A-E were analyzed for statistical significance with Student’s T-test, n = 7–9. F and G were analyzed for significance with a mono-exponential curve fit and an extra sum of squares F-test, n = 7 animals per group; * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.