Final answer:
Congenital heart defects such as patent ductus arteriosus and tetralogy of Fallot can cause tachypnea in an infant 6-8 weeks of age.
Step-by-step explanation:
Tachypnea in an infant 6-8 weeks of age can be caused by congenital heart defects such as patent ductus arteriosus and tetralogy of Fallot. Patent ductus arteriosus is a condition where the ductus arteriosus, a blood vessel that normally closes after birth, remains open and causes increased pulmonary pressure, making respiration difficult. Tetralogy of Fallot is a condition characterized by an opening in the interventricular septum, leading to a mixture of low-oxygen and high-oxygen blood, resulting in a bluish discoloration (cyanosis) and tachypnea in infants.