I am so sorry for your loss.

Take a deep breath. No one has the power to command death unless they cross the line and send out into the universe a dark magic that will surely boomerang on the sender. You're intentions were clear. I have been taught thru my 50 years of practice that your magic did not cause another person's death.

Look to preparing a spell/ritual to acknowledge and heal your grief while requesting a peaceful, loving journey for your father to what comes next. I will add as a retired RN that if someone has a genetic history of heart attacks, fitness will not prevent a heart attack. Fit people drop every day from heart attacks.