NID1 increases heart function post‐MI. A–C) Echocardiography analysis: absolute values of (A) EF and (B) FS after intracardiac injections of saline, HA and 50 µg mL−1 NID1 + HA at 28 days post‐MI/R, and C) parameters were normalized to the baseline at 28 days post‐MI/R. Echocardiography data were analyzed by one‐way ANOVA with Tukey's multiple comparisons test. D–I) Movat pentachrome staining of representative sections of (D–F) HA‐ and (G–I) NID1 + HA‐treated hearts after 28 days post‐MI/R with scar tissue stained in green and yellow. Scale bars: (D,G) 1 mm, (E,H) 200 µm, and (F,I) 100 µm. J,K) Picrosirius Red and Fast Green staining of representative (J) HA‐ and (K) NID1 + HA‐treated heart sections with scar tissue stained in pink. Scale bars: 1 mm. L) Quantification of scar size in Picrosirius Red‐ and Fast Green‐stained serial sections. Whole‐heart scans of every tenth slide throughout the whole heart were analyzed. M–P) Confocal images of αSMA, CD31, and CTNT IF staining of representative (M) baseline, (N) HA‐, and (O) NID1 + HA‐treated heart sections obtained with a 25× magnification (scale bar: 100 µm), and with a P) 63× magnification (scale bar; 50 µm). Q) Quantification of vessel density within the infarct area using images obtained with a 25× magnification. R–U) Images of TuJ1 and CTNT IF staining of representative (R) baseline, (S) HA‐, and (T) NID1 + HA‐treated tissue sections obtained with a 25× magnification (scale bar equal 100 µm), and a (U) 63× magnification (scale bar: 50 µm). V) Quantification of TuJ1+ cells within the infarct area. For all MI/R studies saline mice (n = 3), HA mice (n = 3), NID1 + HA‐treated mice (n = 4) were used, unpaired t‐test. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. LVIDd: left ventricular internal dimension at end diastole, LVIDs: left ventricular internal dimension at end‐systole, LVED: left ventricle end‐diastolic diameter, LVES: left ventricle end‐systolic diameter, EDV: end‐diastolic volume, ESV: end‐systolic volume, EF: ejection fraction, FS: fractional shortening.