by heredity? how will anticipating the development of these disease help in preventive medicine

I think it's more a case of preventative action, i.e, if heart disease runs in families and an offspring is at greater risk, then that individual can reduce their chances of developing CHD(if they haven't already) by maintaining a healthy lifestyle etc...all it basically means is that the person is at more risk of developing CHD than say, an individual with no family history of CHD

I think that more than the disease itself, it is the predisposition to a disease that can be transmitted by inheritance. This predisposition is generically caused by the presence of genetic mutations in important genes involved in a specific pathway, whose malfunction leads to the disease.

For example, the mutation of the gene BRCA1 confers predisposition to breast cancer and it is genetically transmitted. BRCA1 is a protein involved in the detection and repair of damaged DNA; therefore, if a cell with mutBRCA1 is exposed to "insults" that affect the DNA structure, it would not be able to repair the problem and it could become a "cancer" cell and later a "cancer" clone.
Antother example is given by the mutation of genes involved in maintaining the stability of our genome (MMR complex, checkpoint kinase), which could lead to hereditary colon cancer.
Finally, people with Li-Fraumeni syndrome have a mutated p53, which is a "tumour suppressor" protein, as it is able to get rid of lesions "pre-cancerous" cells. These people are predisposed to sarcomas, lymphomas, etc...

Hovever, it is not 100% certain that people with those mutations will develop the disease at some stage of their life, as most of these "mutations" are complicated by a great deal of interplay between genes and environment.

Hope it is not too complicated - I tried to use layman terms...

It sure seems that a lot of diseases do run in families like cancer and diabetis, even some types of heart disease. There was this one guy named Fixx who wrote 'the Complete Runners Hand book'.. his dad had died when he was really young and he lasted longer than his dad but not by that many years.

It sure seems that a lot of diseases do run in families like cancer and diabetis, even some types of heart disease. There was this one guy named Fixx who wrote 'the Complete Runners Hand book'.. his dad had died when he was really young and he lasted longer than his dad but not by that many years.