Theophylline is a bronchodilator used in veterinary therapy that is effective in the management of congestive heart failure, asthmatic bronchitis and chronic obstructive pulmonary disease in animals. Included in the drug classification as smooth muscle relaxant, the medication is active against conditions affecting the respiratory muscles of dogs and cats. Theophylline, the active ingredient contained in the medication helps in relaxing the muscles in and around the windpipe, thereby dealing with the breathing complications due to asthma. The medication effectively works as airway dilator by widening bronchitis tubes to facilitate easy breathing. Theophylline is available only by prescription and comes as tablets, long active capsules and liquid.