Fun game! I didn't realize you could shoot upwards until the final boss! Music is kinda grating imo tho lol. I got 9 hearts by the end, is that all of them?
Glad you had fun. :) Music gets interrupted by sound effects and this is intentional to mimic the single channel limitation of Nokia 3310.
9 hearts are the maximum (I decided on that because it is the largest single digit number, otherwise HP indicator would take additional 8 pixels of width (two additional digits, each 3 pixels wide plus one pixel of spacing: 2x(3+1)=8)), congratulations on finding all additional 6 hearts!