Is the after load resistance what ventricle in heart has to contract against?

Yes, the after load resistance is what the left ventricle in heart has to contract against.

Afterload is the pressure that the ventricles have to overcome to eject blood. It is determined by the systemic vascular resistance (SVR) and the aortic valve resistance. The SVR is the resistance to blood flow in the arteries, and the aortic valve resistance is the resistance to blood flow through the aortic valve.

The left ventricle is the main pumping chamber of the heart. It contracts to eject blood into the aorta, which is the main artery that carries blood to the body. The afterload resistance that the left ventricle has to contract against is therefore determined by the SVR and the aortic valve resistance.