Base of the heart is formed by-
Left Auricle. The left auricle, also known as the left atrial appendage (LAA), is a flap of heart wall on the anterior surface of the left atrium of the heart.
The name auricle comes from the Latin word auricula, which means “ear” and refers to the floppy dog-ear shape of the auricle
Rt. ventricle
LV
LV + RV
RA + LA