Although cats are less likely than dogs to develop heartworm, infection does occur, particularly in areas with a high mosquito infestation. The heartworm parasite is transmitted through mosquito bite and generally lives in the right side of the heart and arteries of the lungs, causing heart failure, blocked arteries and breathing difficulties. To prevent your cat from contracting heartworm, help her maintain a strong immune system with a natural, well-balanced diet free from additives and preservatives and include fresh, raw foods and yeast and garlic to repel mosquitoes. Keep her indoors during late afternoons and evenings, which are the times of greatest mosquito activity and use natural insect repellents such as citronella oil and water. Herbs such as wormwood and cloves help to promote cleansing and to repel parasites. However, it is best to consult with a veterinarian before beginning any type of treatment.