After several years with an anal fissure and using uselessly
many ointments, pills and supplements, etc, I got a total cure thanks to two things: two surgeries (I believe that in very advanced stages of anal fissure, surgery is essential) and in order to avoid recurrence, an adherence to a 100% carnivorous diet. Two years after the last surgery, I am totally healed. The carnivore diet (predominantly meat, eggs and dairy) prevents episodes of either constipation or diarrhea; the stools are always small and soft. For the past two years I haven't eaten any fiber-containing foods.

Glad to read of your success in healing. Thanks for the notes on diet and surgery. I think you are right on those, however I am not a doctor.
Here is what has worked for me and I am currently fissure free:
1) Drink lots of water -- I drink 3 large (~12 oz.) glasses in the morning and three in the afternoon. This became my routine.
2) Get a good night's sleep -- ~7 hours a night so my body could heal.
3) Ointment -- Ma Ying Long Hemorrhoids Ointment worked well. It can be ordered from Amazon.
4) Enema -- Relieved burning after a BM and gave temporary relief. Allowed ointment to work better while sleeping to heal.
Things that did not work for me:
High fiber diet, fiber supplements and over the counter ointments like Preparation H and Anusol (but I do hope they help others if tried).

tx62 wrote:Things that did not work for me:
High fiber diet, fiber supplements and over the counter ointments like Preparation H and Anusol (but I do hope they help others if tried).

I believe that even with the surgeries I wouldn't be cured if I hadn't completely changed my diet. A normal diet, sooner or later, would cause episodes of diarrhea or constipation and "wake up" the fissure. Many foods, especially high in fiber, cause a lot of intestinal disturbances and this has consequences in the anal area.
A carnivore diet is the friendliest and most natural for the gut (after a short period of adaptation). Always eating the same kind of food, you ensure that the stools are always the same and there are no bad surprises.
You will never have again bulky stools, or liquid stools or even flatulence again.
Nor will you ever need any kind of ointment or supplement again to do something as natural as defecating.

For me it was lactulose. Its now been 15 years, after experiencing the condition for 4 or 5 years.