Erythema multiforme (EM) is a skin reaction that comes from an infection or another trigger. EM is a type of allergic reaction. In most cases, it occurs in response to an infection. In rare cases, it is caused by certain medicines or body-wide (systemic) illness. Infections that may lead to EM include:
1 Heart attack. A heart attack can damage the area of the heart muscle that supports the mitral valve, affecting the function of the valve. If the damage is extensive enough, a heart attack can cause sudden and severe mitral valve regurgitation.  Abnormality of the heart muscle (cardiomyopathy).
This can lead to blood leaking backward (regurgitating) into the right atrium. Tricuspid valve regurgitation in children is usually caused by heart disease present at birth (congenital heart disease), and Ebstein's anomaly is the most common congenital heart disease that causes the condition.