Channel which drains major pa of myocardium:

Coronary sinusIt is a collection of veins joined together to form a large vessel that collects blood from the heamuscle (myocardium).It delivers deoxygenated blood to the right atrium, as do the superior and inferior vena cava.The coronary sinus opens into the right atrium, at the coronary sinus orifice, between the inferior vena cava and the right atrioventricular orifice.It returns the blood from the substance of the hea, and is protected by a semicircular fold of the lining membrane of the auricle, the valve of coronary sinus (or valve of Thebesius).