The heart’s internal pacemaker beats by:
an internal implant that sends an electrical impulse through the heart
the excitation of cardiac muscle cells at the sinoatrial node followed by the atrioventricular node
the excitation of cardiac muscle cells at the atrioventricular node followed by the sinoatrial node
the action of the sinus

what image you forgot to include it.

the answer is otpion c) understanding

he wants to be heard one more time. he wants to be understood. he needs the truth one more time.

cuz he is really really short, assuming an unorthodox and inherently unlucky configuration of elevator buttons…

explanation:

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.