Checking if a value is contained in a MutableBinaryHeap?

Hello guys, I need to test if a value is contained in a MutableBinaryHeap.

I may have the following Tuple t:

6-element Vector{Tuple{Int64, Float64}}:
 (1, Inf)
 (2, Inf)
 (3, Inf)
 (4, Inf)
 (5, Inf)
 (6, Inf)

For the Tuple case I can just do:

a=first.(t)

And check whether a value is contained in a.
The problem is that I need to do this test on a MutableBinaryHeap.

I have the heap h

MutableBinaryHeap((1, 0.0), (2, Inf), (3, Inf), (4, Inf), (5, Inf), (6, Inf))

and doing

c=first.(h)

gives the following error:

ERROR: MethodError: no method matching iterate(::MutableBinaryHeap{Tuple{Int64, Float64}, Base.Order.By{typeof(last), Base.Order.ForwardOrdering}})

Any idea on how to test is a value is contained on the first element of a MutableBinaryHeap?

Thank you so much in advance.