Cathepsins B and L have both been implicated in COVID-19 and other viral myocarditis (Wang et al. 2018; Hashimoto et al. 2021; Zhao et al. 2021; Ding et al. 2022; Huang et al. 2022); and both exhibit Zn2+ responsiveness ex vivo. Here, CTSB is linked to COVID-19.