Oxygenated: lungs → left heart → bedsDeoxygenated: beds → right heart → lungsRotameter floats: flow to each bedThe two circuits in series, as a mock circulatory loop. Not to scale: a bench model (ruler: 1 tick = 1 cm of the bench); in the body the vessels run ~100,000 km. Right pump → lungs → left pump → five beds in parallel → right pump. Meters, left to right: brain, gut and liver, kidneys, muscle, skin and the rest; each has its own full scale (1, 1.5, 1.5, 15 and 4 L/min). At rest the heart beats 70 times a minute and pumps 4.9 L/min; in heavy exercise ~170 beats and ~17.5 L/min, and muscle's share rises from a fifth to over two thirds while the brain keeps its 0.75 L/min. The lungs always take the whole output. With ~5 L of blood, one lap takes about a minute at rest and 17 s at full effort. The pumps beat at the true rate; the blood is shown ~15× faster.
~5 L/min静息心输出量（70 次 × 70 ml）cardiac output at rest (70 beats × 70 ml)~17–20 L/min剧烈运动时的心输出量cardiac output in heavy exercise~5 L成人血量adult blood volume~1 min静息时血液循环一周one lap of the circulation at rest20% → 70%运动时肌肉所占心输出量muscle's share of output, rest → exercise0.75 L/min脑血流，运动时基本不变brain blood flow, held in exercise