Considering , your app crashes every time giving "OutOfMemoryError"
DVM starts by allocating a small heap, after every garbage collection cycle it checks for free heap and compares it to the total heap memory and adds more memory in case that the difference is too small. So Heap can be increased or decreased at runtime as per Dalvik VM's requirement by OS.
So, when their is enough memory available in the system your app didn't get crashed when the memory shoots up to 80mb.(Assuming 64MB is not the hard limit of heap size)
Yes there is a hard limit on the heap size of every device which can be increased by using "LargeHeapSize = true" , but this might be too costly in terms of app performance as increased heap size is directly proportional to the time taken by the garbage collection process(as GC now have to traverse more objects inside bigger heap). So it is a big "NO,NO" until unless you exactly know what and why are you going for larger heap size.
on what factor heap size depends:
Heap size mainly depends on the resolution of the device you are
using, as more resolution needs larger images/bitmaps size to fit
in.(more pixels = needs more memory to incorporate)
Although, I didn't got through any written proof of this.. As per my
understanding Heap size also depends on the RAM size. Since, bigger
RAM size will allow more flexibility of multitasking and lesser
chances of getting the "OutOfMemoryError"
In case you needs to know exact amount of heap memory you can use, ActivityManager.getMemoryClass(). This method returns an integer indicating the number of megabytes available for your app's heap
ActivityManager.getLargeMemoryClass() for larger heap size