Final answer:
The coronary sinus joins back up to the heart at the right atrium, which collects deoxygenated blood from the systemic circuit including blood that has circulated through the heart tissue.
Step-by-step explanation:
The coronary vein, specifically the coronary sinus, joins back up to the heart at the right atrium. The right atrium serves as the collecting chamber for deoxygenated blood returning to the heart from the systemic circuit, which includes the blood that has traveled through the heart's own muscular tissue.
Veins like the small cardiac vein, as well as the great cardiac vein, ultimately drain into the large coronary vein, or the coronary sinus. This blood is then channeled into the right atrium from there through the opening of the coronary sinus on the posterior surface of the atrium. Also, to note, the superior and inferior venae cavae drain systemic blood into the right atrium.