What cardiac diseases or conditions that can be caused by anemia ? how long does it take for anemia to affect the heart ?

Depends: Red blood cells carry oxygen to the tissues of the body. In anemia, the heart tries to compensate for a lack of oxygen delivery by pumping the blood faster. If the heart cannot cope with the increased demand, heart failure may occur. If the heart muscle doesn't get enough oxygen to meet its demands a heart attack can happen, but only with very severe anemia or a diseased heart.

Volume overload: Main concern is volume overload-->the lower the hemoglobin, the more blood the heart has to pump to satisfy the body's O2 demands. The more severe the anemia, the more the heart's workload increases, & the overall health of the heart informs how well it handles this extra workload. Your question is hard since the degree of anemia & the health of the heart will set how long the heart tolerates it.

Unusual to affect he: Anemia rarely causes any heart damage although the Heart has to work harder in patients who have more than mild Anemia and that too if they have chronic Anemia like in patients with Sickle cell disease or other hemolytic anemias for which there is no cure. Most times this does not mean that the heart is damaged or diseased due to anemia.