A prolonged heat wave can be tough on anyone, but if you have heart disease you need to be especially careful when it's hot. This is because the high environmental temperatures can put excess stress on your heart, and also because it is often easier for people with heart disease to develop potentially dangerous heat illness.
In a hot environment, the body attempts to dissipate excess heat (mainly by sweating, and by radiating heat from the skin) to maintain a reasonably normal body temperature. The need to dissipate heat places added stress on your cardiovascular system, and this stress may cause the symptoms of your underlying heart disease to worsen. For instance, a person with coronary artery disease may develop angina; or a person with heart failure may have more shortness of breath.
In extreme heat, the body's attempts to dissipate heat can become overwhelmed, and if this happens the body's temperature begins to rise. The increase in body temperature, along with the dehydration and electrolyte imbalances that most often accompany it, produces heat illness.
Heat illness is a continuum of disorders ranging from heat rash, to heat cramps (muscle cramps), to heat exhaustion (cramps, weakness, dizziness, nausea and vomiting, headache), to heat stroke (body temperature of 106 degrees F. or higher, plus neurological symptoms such as seizures, disorientation, or coma). Heat stroke can be fatal.
Unfortunately, the drugs that are often used in treating heart disease can make it more difficult for your body to dissipate excess heat when temperatures are very high, and thus, may make heat illness more likely. Almost any cardiovascular medication can make you more prone to heat illness, but this is especially true with beta blockers, calcium channel blockers, and diuretics.
So, while everyone should take precautions during a heat wave, it is especially important to do so if you have heart disease. The most important thing to do is to stay in a cool environment during the heat of the day. If you don't have air conditioning, consider going to the mall, to a church, or to a neighbor's. Avoid exertion, since the calories you burn during exercise will just produce that much more heat that your body will need to dissipate. And stay very well hydrated on hot days, preferably by drinking water (and avoiding caffeine, which is a diuretic).
If you should develop signs of heat illness, such as muscle cramps or nausea, call your doctor immediately.
And DO NOT stop any of your cardiac medications on your own, without checking with your doctor first.