MH stands for Malignant Hyperthermia - it is a dominant disease 
Genetic Testing is Available
MH causes severe tying up and possible death in affected horses after exposure to certain types of anesthesia. (if you have an MH horse you must make sire your vet knows about it before performing any surgery involving an anesthetic) Other symptoms include high temperature, erratic and heavy sweating, a rapid heart rate, irregular breathing and rigid muscles - these are often brought on by stress from exercise, excitement, trailering, change of ownership, etc Emergency cases of MH can be treated with dantrolene.
MH affects Quarter horses and related breeds and has been traced back to a mare named Miss Ogallala (98% of MH horses trace to her) - we are still searching for a couple other very rare lines of MH in Quarter horses.
*** If your horse has been diagnosed with MH please consider sending us the pedigree, especially if Miss Ogallla is not an ancestor.
*** If your horse has died under anesthetic please consider sending us the pedigree