Ex Vivo Myocardial Infarction Model in the Crystalloid-Perfused Mouse Heart

Experimental myocardial infarction (MI) is commonly modeled in animals through transient occlusion of the left anterior descending (LAD) coronary artery or, at the cellular level, by hypoxia-reoxygenation protocols. As an alternative organ-level model of ischemia, the Langendorff-perfused heart has remained a cornerstone tool for investigating the effects of physiological perturbations and pharmacological interventions on cardioprotection. Here, we present the basic methodology and fundamental rules required for establishing a regional myocardial ischemia/reperfusion model in the isolated mouse heart. In brief, following cardioplegic arrest, the LAD was ligated after a brief flush with ice-cold PBS. The heart was then mounted on a Langendorff apparatus and perfused with a nutrient-rich oxygenated buffer at 37°C under a constant perfusion pressure of 110 cmH₂O. The length of myocardial ischemia was induced for 30, 45, 60, 90 and 120 min followed by 90 min of reperfusion. Cardiomyocyte viability and infarct size were assessed by using microscopic 2,3,5-triphenyltetrazolium chloride (TTC) staining approach. We demonstrated that the ex vivo MI model reliably yielded reproducible myocardial injury, characterized by a progressive loss of viable cardiomyocytes within the infarct region as ischemic duration extended. In addition, at least 30 min of reperfusion was required to achieve clear TTC-based delineation of the infarcted myocardium. This approach bypasses systemic variables, thereby allowing researchers to evaluate directly cardiac effects in the absence of extrinsic regulatory influences, such as circulating humoral factors and immune cell infiltration, that may confound MI progression, and to test localized pharmaceutical interventions. Thus, the ex vivo MI model represents a useful platform for investigating cardioprotective mechanisms that act directly on cardiomyocytes.