Several studies, mainly based on polysomnography, conducted among elderly participants have shown that sleep efficiency and total sleep time are decreasing with age. Quality and quantity of sleep is affected by ageing. As a consequence, elderly individuals often show excessive daytime sleepiness.
The literature provides a very thorough list of possible cause of decreased quality and quantity of sleep with age, most common causes though seem to be related to chronic diseases such as joint diseases and chronic pains but also cardiac and pulmonary diseases. Concerning the latter, patients with pulmonary and cardiovascular diseases may suffer from sleep apnea (you can test this by answering the “Epworth Sleepiness Scale”, available on the internet). Your questions provides to few details to answer this, and maybe you should check with your family doctor. Also, some medications have been linked to sleep disturbances such as beta-blockers and diuretics (which are often prescribed in the case of heart problems).
However, sleep disturbances may also affect elderly individuals who are in good health. In the last decades, several hypotheses have been suggested to explain the alteration in circadian rhythm in the elderly. For example, one of the organ involved in circadian rhythm synchronisation, the suprachiasmatic nucleus, shows a decline in its function with age. Also, age is associated with a decrease in melatonin, a hormone essential in the regulation of circadian rhythm.
As you can see there are many reasons for day sleepiness in the elderly. If your daytime sleepiness impacts on your daily life (and on your social activities), you may wish to consider seeing your family doctor.
Sources:Cooke JR, Ancoli-Israel S. Normal and Abnormal Sleep in the Elderly. Handbook of clinical neurology / edited by PJ Vinken and GW Bruyn. 2011;98:653-665. doi:10.1016/B978-0-444-52006-7.00041-1.