Heartworm is a worm that resides in the heart and lungs of infected dogs and cats. It is carried by mosquitos who transmit heartworm larva into the bloodstream of the pet when they bite them. These larva then develop into adult worms that over time cause heart disease and respiratory problems in dogs. In cats, the signs can be more vague including vomiting, coughing, weight loss and sudden death. Fortunately this is a preventable disease and there are a number of excellent monthly heartworm preventatives available through your veterinarian. These products when given year-round provide outstanding protection against heartworm disease, and many also protect against several important intestinal parasites that can infect dogs, cats and people. There are even all in one products that prevent heartworm, intestinal worms, ticks and fleas. Your veterinarian can help you decide which product is best for you and your pet.