Effect of ARNI and ivabradine on hydroxyproline concentration in soluble and insoluble collagenous proteins and on the total hydroxyproline concentration (A), and on hydroxyproline content in the soluble and insoluble collagenous proteins, and on the total hydroxyproline content (B) in the left ventricle in SHRs after six weeks of treatment. ARNI, sacubitril/valsartan; C, Wistar controls; IVA, ivabradine; SHRs, spontaneously hypertensive rats. Results are presented as means ± SEM. n = 15 per group. One-way, two-tailed ANOVA followed by multiple comparisons with a Bonferroni post-hoc test; * p < 0.05 vs. C; # p < 0.05 vs. SHR.