How does a rat's heart beat? - briefly
A rat’s heart contracts at roughly 300–400 beats per minute, initiated by electrical impulses from the sino‑atrial node that travel through the atria and ventricles. The cycle consists of rapid depolarization, contraction, repolarization, and relaxation, occurring faster than in larger mammals due to the animal’s small size.
How does a rat's heart beat? - in detail
The rat heart operates through a sequence of electrical and mechanical events that generate a regular pulse. An impulse originates in the sino‑atrial (SA) node, the intrinsic pacemaker located in the right atrial wall. The SA node depolarizes spontaneously at a rate of 300–500 beats per minute in adult rodents, establishing the baseline rhythm.
After initiation, the depolarization wave spreads across both atria, causing atrial contraction and pushing blood into the ventricles. The atrioventricular (AV) node delays the signal briefly, allowing complete ventricular filling before transmission to the His‑Purkinje network. The rapid conduction system distributes the impulse throughout the ventricular myocardium, producing a coordinated contraction that ejects blood into the pulmonary artery and aorta.
Mechanical phases of the cardiac cycle include:
- Isovolumetric contraction – ventricular pressure rises while all valves remain closed.
- Ejection – semilunar valves open, blood is expelled.
- Isovolumetric relaxation – ventricles relax, pressure falls, all valves closed.
- Filling – atrioventricular valves open, ventricles receive blood.
Autonomic regulation modulates the intrinsic rate. Sympathetic stimulation increases SA‑node firing frequency and contractility, raising heart rate up to 600 bpm during stress. Parasympathetic (vagal) input slows the pacemaker activity, reducing rate to about 250 bpm during rest.
Electrocardiographic recordings in rats display a markedly shortened PR interval and QRS complex compared with larger mammals, reflecting the rapid conduction velocity of the Purkinje system. The QT interval scales with heart rate and can be corrected using species‑specific formulas.
Experimental measurements typically employ telemetry implants or surface electrodes under anesthesia. Data acquisition systems sample at high frequencies (≥1 kHz) to capture the brief cardiac events accurately.
In summary, the rat cardiac rhythm is driven by a high‑frequency SA node, rapid atrioventricular conduction, and tight autonomic control, resulting in a fast, efficient pump suited to the animal’s metabolic demands.