• Must have provided informed consent in a manner approved by the Investigator's Institutional Review Board (IRB) prior to any study-related procedure being performed. If a participant is unable to provide informed consent due to his/her medical condition, the participant's legally authorized representative may consent on behalf of the study participant, as permitted by local law and institutional Standard Operating Procedures;

• Aged greater than or equal to 18 years at the time of informed consent;

• Recent use of an FDA-approved immune checkpoint inhibitor (ICI, defined as administered an immune checkpoint inhibitor ≤ 6 months of myocarditis diagnosis), alone or in combination with other cancer therapies (i.e. chemotherapy, radiation therapy or targeted therapy). The FDA-approved ICI could be given as part of a clinical trial but not in combination with a new investigational agent which may cause myocarditis;

• A diagnosis of myocarditis.

• Hospitalized at the time of randomization;

• On 1000 mg of solumedrol per day for myocarditis or with an intent to initiate 1000 mg of solumedrol per day for myocarditis within 24 hours of first administration of study drug;

• Serum evidence of ongoing myocardial injury: Serum evidence of ongoing myocardial injury will be defined as an institutional troponin (either conventional or high-sensitivity troponin I or T, using the standard institutional assay) with a value that is ≥5 times the upper limit of the reference standard normal for that institution. The troponin assay may be adjusted based on sex depending on institutional standards. This value of troponin of ≥5 times above the institutional upper limits of normal value must be noted within 10 days prior to potential randomization. The 10-day period can be in the outpatient or inpatient setting. For example, a participant with a troponin value that on one occasion was ≥5 times the upper limits of institutional normal in the 10-day window prior to potential randomization (whether in the inpatient or outpatient setting), but later decreases below that threshold, typically due to starting corticosteroids, would still be considered eligible;

• The following laboratory parameters, not older than 48 hours at the time of randomization, and measured as part of usual care:

‣ Total white blood cell (WBC) count \>2,500/μl

⁃ Absolute neutrophil count (ANC) \>1,500/μL

⁃ Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \<20 times the upper limit of the institutional normal ranges;

• Women of childbearing potential (i.e., not postmenopausal, or surgically sterilized) must have a negative highly sensitive urine or serum pregnancy test prior to randomization. Participating women of childbearing potential must be willing to consistently use effective methods of contraception from screening until at least 90 days after administration of the last dose of study drug. Participating men must also be willing to consistently use effective methods of contraception from screening until at least 90 days after administration of the last dose of study drug; and

⁃ Must be willing and able to abide by all study requirements and restrictions.