Heaves is an old colloquial name for a common respiratory problem in stabled horses worldwide. This somewhat ambiguous term has come to refer to a syndrome of clinical signs, and related patho-physiological abnormalities, that is better referred to as 'Chronic Pulmonary Disease', or 'Chronic Obstructive Pulmonary Disease', of horses. In recent years, attempts have been made to classify COPD is horses into a number of specific pathologic categories, including: chronic bronchitis and bronchiolitis, chronic asthmoid bronchitis and bronchiolitis, interstitial pneumonitis or alveolitis, alveolar emphysema, or combinations of these. Most likely all are manifestations of clinically and functionally similar disease entities representing different stages in the pathogenesis or different individual responses.