How can one acquire a sound heart to treat severe psychological problems?

A sound heart is one that is free from polytheism (shirk (definition)), malice, hatred, envy, avarice, and arrogance, and from every desire that contravenes Allah's command and prohibition, and from every doubt that contradicts His revelation, and from every affliction that distances it from Allah. The way to attain it is by seeking Allah's help, striving against and holding oneself accountable, adhering to the commands of the Sharia (definition), keeping company with the righteous, and remembering death and accountability.