What sort of heart and qualification required to completely surrender to a spiritual master?
Krishna describes in Bhagavad Gita how one should approach a realized spiritual master (Bg 4.34). He indicates three components: submission, inquiry and service. One should approach the spiritual master with all humility, hear from him submissively and inquire from him to get a clear understanding about the spiritual science. Inquiring alone is not sufficient, but one must also render service to the spiritual master according to what one has heard and try to please him. One should be prepared to render menial service to the spiritual master and follow his instructions.
If one is very sincere to know Krishna, He will send His mercy in the form of a representative, to provide exactly the kind of spiritual upliftment the soul requires.