During pregnancy, the fetal lungs are not used for breathing—the placenta does the work of exchanging oxygen and carbon dioxide through the mother's circulation. With the first breaths of air the baby takes at birth, the fetal circulation changes.
Prosthetic heart valves are classified as either mechanical (constructed of entirely synthetic material) or biologic (human, porcine, bovine). All prosthetic valves are associated with complications ranging from structural failure and thrombosis to systemic embolization, hemolysis, and endocarditis. A paravalvular leak occurs when a portion of the prosthetic valve becomes unseated from the valve annulus. It is more common with mechanical valves.