Intracardiac implantation of MDSC improved the LVEF and reduced infarction size after LAD, but concurrent chronic sildenafil abrogated these effects. Intracardiac injection of saline or MDSC was conducted at 1 week (n = 7/group). Sildenafil was then given continuously in the drinking water until sacrifice at 4 weeks. Top: Ejection fraction before MI (basal), and at 1 and 4 weeks. NaCl: control injected with saline; MDSC: injection with MDSC; MDSC + S: MDSC with sildenafil. Bottom: quantitative image analysis of infarction area by Picrosirius red histochemistry. Statistical differences are stated for untreated versus basal, and MDSC, and MDSC + sildenafil versus untreated; *p < 0.05.