my %hash = (
    4 => 20,    # second highest key
    2 => 40,    # second highest value
    3 => 30,
    1 => 50,
    5 => 10,
);

# second highest value
print ((sort values %hash)[-2]);

# key based on the second highest value
print ((sort { $hash{$b} <=> $hash{$a} } keys %hash)[1]);