Ordinarily, all these factors are smoothly integrated to meet the variations of cardiac output required by physical activity, emotional stress, digestion, and ambient temperature. Disturbances in the rate and the synchronization of cardiac contraction are generally termed arrhythmias. The other two chambers, the ventricles, form the tapered body of the heart and have much thicker walls. The atrium and the ventricle on each side act as a functional unit. The right atrium and the right ventricle receive blood from the body as a whole by way of the systemic venous system.
Blood is pumped from the right side to the lungs via the pulmonary arterial system.
The chambers of the left side receive blood from the lungs by the pulmonary venous system and propel it to the body through the systemic arterial system, thus completing the circuit. Electrical activity from the heart emits small currents on the body surface. However, these skeletal muscle currents are not visible in the ECG when the subject is lying at rest. The surface currents produced by cardiac activity are extremely small, so that an electrical amplifier is necessary to generate visible complexes on a recording. The electrocardiograph transmits the emitted electrical activity to a sensing component through wires connected to electrodes that are placed on the skin.