(1) Background: Emerging data indicate that the ongoing COVID-19 pandemic may result in long-term cardiovascular complications, among which long COVID-19 myocarditis seems to be one of the most dangerous. Clinical presentation of cardiac inflammation ranges from almost asymptomatic to life-threatening conditions, including heart failure (HF) in different stages. (2) Methods: This is a retrospective case-series study that includes three adults with different clinical presentations of heart failure on grounds of myocarditis after initial COVID-19 infection. (3) Results: All patients had new-onset symptomatic HF of various severity: from a moderately reduced left ventricular ejection fraction in one patient to significantly reduced fractions in the remaining two. Moreover, complex ventricular arrhythmias were present in one case. All patients had confirmed past myocarditis in cardiac magnetic resonance. With optimal medical treatment, cardiac function improved, and the symptoms subsided in all cases. (4) Conclusions: In COVID-19 patients, long COVID myocarditis may be one of the severe complications of this acute disease. The heterogeneity in clinical symptoms and a paucity of specific diagnostic procedures expose the patient to the significant risk of misdiagnosing and further HF development.