In 54%, yes, that's right, cardiac abnormalities were detected among 81 (54%) of 151 patients with follow-up cardiac MRI when Kracalik et al. looked at outcomes at least 90 days since onset of

myocarditis after mRNA technology COVID vaccination in adolescents and young adults in the USA

‘Most patients were admitted to hospital after an initial diagnosis of myocarditis (484 [93%] of 519 patients).’

‘In the ten patients with abnormal ambulatory rhythm monitoring results, we found eight (80%) had atrial, supraventricular, or ventricular arrhythmia, three (30%) had a conduction delay or block, and five (50%) had frequent atrial or ventricular ectopy. Of these 10 patients, three (30%) had evidence of late gadolinium enhancement on follow-up cardiac MRI; of the three with evidence of late gadolinium enhancement, two (67%) had evidence of an atrial, supraventricular, or ventricular arrhythmia. Among the 151 patients who had cardiac MRIs during outpatient follow-up, 81 (54%) patients had one or more abnormalities. Abnormal cardiac MRI findings included the presence of late gadolinium enhancement (71 [47%] patients), inflammation or oedema (22 [15%] patients), or wall motion abnormalities (six [4%] patients; figure 3, appendix 1 p 9).’

SOURCE:

More evidence:

In the Thai study below by Mansanguan et al., of n=301 students who got the Pfizer injection, 29% evidenced cardiac symptoms, including myocarditis.