Adverse effects to transfusion with red donor blood cells are potentially life-threatening. Due to screening, transmission of infectious diseases has decreased; however, the risk is still present. Various immune reactions are common including simple allergic reactions as well as devastating conditions such as transfusion-related acute lung injury and circulatory overload in patients with heart disease. Knowledge of the clinical signs of transfusion-related complications is important for clinicians in order to provide the best possible treatment.