Electrical Activity in the Heart

The Cardiac Cycle

The cardiac cycle is a sequence of events that take place in a complete heartbeat.
The heart is divided into two separate pumps: the right atrium and ventricle (which pump blood to the lungs) and the left atrium and ventricle (which pump blood to the rest of the body).
The cycle involves three stages: Atrial systole, Ventricular systole, and Cardiac diastole.

Electrical activity is initiated by the sinoatrial node (SA node), also known as the pacemaker.
The electrical impulses generated by the SA node triggers the muscles in the atria to contract (atrial systole).
These electrical impulses then reach the atrioventricular node (AV node), which has a slight delay to allow the atria to finish contracting.
After the delay, the AV node sends the impulses along the bundle of His and then into the Purkinje fibers spreading the wave of excitation to the ventricles causing them to contract (ventricular systole).

Electrocardiogram (ECG) provides a record of the electrical activity of the heart.
ECG consists of P wave (representing the excitation of the atria), the QRS complex (representing ventricular excitation), and the T wave (representing ventricular relaxation).
An irregular ECG reading can indicate various heart conditions, such as arrhythmias and myocardial infarction.

During exercise, the body requires more oxygen and energy. This triggers an increase in heart rate and stroke volume, thus increasing cardiac output.
This increased demand is met via the nervous system, predominantly the sympathetic nervous system, which accelerates the heart rate.
Regular physical activity strengthens the heart muscle, reducing the risk of cardiovascular diseases.

Resting heart rate is a person’s heart rate when they are at rest. It is a key indicator of cardiovascular health, lower resting heart go hand in hand with efficient heart function and cardiovascular fitness.
Factors such as age, health condition, fitness level, and medication usage can affect resting heart rate.
A well-trained athlete might have a normal resting heart rate closer to 40 beats a minute.