Generally speaking (and I must speak generally since I am not able to examine Kiki in person), given Kiki's history of heart worm infection and now an enlarged belly and decreased energy/appetite, I am concerned that Kiki has gone into right-sided heart failure. Right-sided heart failure occurs when the right side of the heart has do extra work for too long such as pumping against increased pressure (as in the case of heart worm infection, where the adult worms are blocking up the outflow tract of the right side of the heart). Eventually the muscles of the heart grow weak and can no longer overcome the pressure needed to get past the adult heart worms. When the right side of the heart fails, fluid backs up through the vena cava (the large vein connecting the abdominal organs to the heart) and into the abdomen. This fluid build up leads to the enlarged (pot belly) appearance of the abdomen. It also makes it hard for Kiki to breathe effectively, which causes a further decrease in energy level.
Right-sided heart failure can be managed with medications, but generally it is only a matter of time before Kiki's quality of life declines and you will be faced with the difficult decision to let him go. He is also at risk of something called Caval Syndrome, which occurs when the adult heart worms block blood flow to and from the heart. This causes sudden onset labored breathing, pale gums, and severe illness. Dogs with caval syndrome cannot survive without surgery to remove the worms.
My recommendation is to take Kiki in to see his veterinarian tomorrow morning. They can prescribe medications to help his heart beat more effectively. You can also discuss heart worm treatment called Immiticide. This is an injection that kills adult heart worms. It is dangerous and carries complications, and it may or may not be indicated in Kiki's case given that his heart muscle is failing (you and your veterinarian will have to decide on this). If Kiki's condition declines overnight, please seek emergency veterinary care for him as needed.
I'm sorry to be the bearer of bad news. I can tell how much you love him and it's heartbreaking when our pets get older and become sick. I wish you and Kiki the best.