Answer: searching for what gives the heart fulfilment can be tasking.
Explanation: Santiago isn't literally in a conversation with his heart, what the writer really wanted the readers to understand is that finding true fulfilment of the heart is a constant struggle and can be a very tasking act. The heart (feeling) can be very tricky if one doesn't really take time to understand it, by understanding it, you can begin to find what exactly satisfies it. But in all, it is a hard thing to do.
