All AAS use will cause left ventricular thickening. This is different than left ventricular thickening from exercise. Exercise such as running induces an outward growth of the heart; keeping the chamber size the same. AAS use causes inward growth of the heart, which decreases left ventricular volume and there for ejection fraction similar to HfRef (heart failure reduced ejection fraction).
Less chamber size means your heart has to work harder to move blood. It also means you can end up getting a backlog of blood built up in the pulmonary veins. It also means that the muscle becomes quite inelastic, and requires more blood flow which it may not be able to get, so you could go ischemic which you’ll feel mostly after exercise but probably not at rest until it’s too late. This can lead to arrhythmias, heart failure etc.
Also, if there’s a backup of blood you can get pulmonary vein stenosis which causes all sorts of issues but ultimately leads to heart failure as well.