During systole the ventricular myocardium gets its oxygen supply mainly from?

During systole, the ventricular myocardium is contracting and the coronary arteries are compressed, reducing blood flow to the heart muscle. Therefore, the ventricular myocardium does not get its oxygen supply mainly from the coronary arteries during systole. Instead, the ventricular myocardium gets its oxygen supply mainly from the Thebesian veins during systole.

Thebesian veins are small veins that connect the ventricular chamber to the coronary sinus. During systole, when the ventricular pressure is high, the Thebesian veins are compressed and blood is forced out of the ventricular chamber into the coronary sinus. This blood then flows through the coronary arteries and supplies oxygen to the ventricular myocardium.