It means "this my loved heart". If you said "Está mi corazón
enamorado" it would mean "It is my heart in love".
"Estás mi corazón enamorado" would be "You are my beloved
heart", although you would normally use the verb "ser" here. "Eres
mi corazón enamorado". It means the same thing, but impled a
permanant condition.