The term cardiomyopathy refers to diseases of the heart muscle, including structural disorders and functional disorders; generally speaking, it is any disease that affects heart.
Myocarditis refers to diseases that cause inflammation of the heart muscle e.g. infections.

Myocarditis
When the heart is involved in an inflammatory process, often caused by an infectious agent, myocarditis is said to be present
Inflammation may involve the myocytes, interstitium, vascular elements &/or pericardium
Characterised by isolated pockets of inflamed & necrotic myocardial cells
Myocardial involvement may be local or diffuse, but the myocardial lesions are generally randomly distributed in the heart & thus the clinical consequences are dependent on the size & number of lesions and the location of the lesions; a small single lesion residing in the conductive tissue may result in a fatal
arrhythmia
May be chronic or acute
Usually of sudden onset
Symptoms include fever, malaise, anorexia, leucocytosis, chest pain, ventricular failure, shock, sudden death

Aetiologies of Myocarditis
Occurs secondary to: i) viral [measles, mumps, influenza]; ii) bacterial [diphtheria]; iii) fungal [aspergillosis]; iv) protozoan [toxoplasmosis, trypanosoma]; v) roundworm [trichinosis]; vi) rheumatic fever; vii) serum sickness; viii) chemical agent [lead]; ix) collagen disease; x) radiation; xi) metabolic [uremia];

Infectious agents cause myocarditis by 3 mechanisms:
1. invasion of myocardium
2. production of myocardial toxin e.g. diphtheria
3. immunologically mediated myocardial damage e.g. rheumatic fever

Relationship of myocarditis to cardiomyopathy
cardiomyopathy: any disease that affects the heart; greatly enlarged heart with no evidence of valvular disease, hypertension or CAD
http://www.perfusion.com.au/CCP/Pathophysiology/Myocarditis....

Types of cardiomyopathy:
1) Primary or Idiopathic (Hypertrophic, Congestive (dilated), Restrictive, ntermediate or Intergrade)
2) Secondary (Metabolic abnormalities, Infiltration of heart muscle, Physical agents, Toxins, Fibroplastic change in
heart muscle, Inflammation of the
heart muscle, Genetically inherited
disorders, Hypersensitivity and some other causes)
http://www.provet.co.uk/health/diseases/cardiac-cardiomy.htm