A heart consists of two pumps, each made of two chambers. The right atrium squirts oxygen-depleted blood from the body into the right ventricle, which pumps it to the lungs. The left atrium squirts aerated blood from the lungs into the left ventricle, which pumps it out to the body. With each heartbeat, the two small atria contract together, then the two large ventricles, making the beating sound.
A typical athlete’s heart churns out 6 to 8 gallons (25 to 30 litres) of blood per minute. In comparison, the best man-made heart can pump about 2.6 gallons (10 litres) per minute and lasts for about 200 million beats – or about 5 years.
A heart is difficult to imitate because it is a soft, wet, contractile muscle – unlike any technology developed thus far. A man-made heart is a battery-powered motor that either drives a piston, or drives a fan blade that sits immersed in a hydraulic fluid, moving a rotary valve. A good man-made heart, it seems, is hard to find.
