The subordinate clause introduced by ainda que, a concessive clause, describes an event that hypothetically can or could prevent the event described in the main clause from happening without actually doing it.
1) Even if he here, he does nothing.
2) Even if he were here, he wouldn't do anyting.
3) Although he is here, he does nothing.
1) describes a general relationship. Every time he is there, he does nothing. 2) Describes a hypothetical situation in the past. At a certain moment he is not there, but even if he were there, he wouldn't do anything. Case 1) requires the presente do conjuntivo in Portuguese, case 2) the imperfeito do conjuntivo. In case 3) we don't have a hypothetical situation. He is not there, but even if this were the case, he wouldn't do anything. Although there is no need to use the conjunctive in this case, in Portuguese the conjunctive is used. In Spanish it is different. We have the same conjunction for although and even if and the distinction in meaning is made by the mood used. In Portuguese the distinction in made using a different conjunction, embora = although, ainda que = even if, but both of them require the conjuntivo.
Ainda que eu possa fazer isto, n�o o farei.
Even if I could do it, I don't do it.
Embora eu possa fazer isto, n�o o farei.
Although I can do it, I don't do it.
Eu posso fazer isto, mas n�o o farei.
I can do it, but I don't do it.
ainda even if
� impressionante, ainda que seja eu quem o diga.
It's impressing, even if it's me who says that.
H� 10 anos que estou s�, ainda que esteja casada.
Even if I am married, I ame lonesome since ten years.
Ainda que o tempo passe eu continuo com voc� em meus pensamentos.