Marginal zone B cell deficiency and marginal zone B cell-specific deletion of miR21 or HIF-1α improve cardiac function via the upregulation of TLR-dependent expression of CCL7 after MI, indicating that the miR21/HIF-1α axis is essential for guiding marginal zone B cell function to mobilize the pro-inflammatory monocytes into the ischemic myocardium. Here, HIF1A is linked to myocardial infarction.