Benefit of CoQ10 for heart function, blood pressure, and for cardiovascular conditions - Coenzyme Q10 is sold as 30 mg, 60 mg, and 100 mg. You can even find 200 mg and 300 pills, is there a risk of overdosing?
CoQ10 is a nutrient of benefit as a good antioxidant and for heart tissue

CoQ10 is a powerful antioxidant which is of benefit for normal heart function and cellular energy production. Co Q10 is a nutritional supplement used around the world as a heart energizer. In some cases of heart problems, there is an associated deficiency of CoQ10. Co Q-10  is a strong antioxidant. Like vitamins, it is a nutrient your body must take in to feed your cells so your body can operate at an optimum level. It is present in small amounts in food, notably seafood, and is produced by all cells of the body. Japanese scientists have synthesized CoQ-10 into a raw material that is put into supplements. Many heart patients use CoQ10 supplements in dosages ranging from 30 mg a day to 100 mg a day or more.

CoQ10 - 50 mg, 60 capsules
Physician Formulas

You can learn more about CoQ10 here, and you can purchase CoQ10 50mg at Physician Formulas.

Various companies sell CoQ10 products, including:
CoQ10, 60 mg, Nature's Way
CoQ10, 30 mg, Doctor's Best
Coenzyme Q10,  100 mg, Natural Factors - Natural Factors easy-to-swallow Coenzyme Q10 softgel capsules contain a  high potency formula consisting of 100 mg of Coenzyme Q10 in a base of rice bran oil for enhanced absorption.  Coenzyme Q10, also called CoQ10 or Ubiquinone is a natural substance essential to cellular energy production.  It is an antioxidant which scavenges free radicals throughout the body.  It is also involved in maintaining normal heart function.  CoQ10 works well with Vitamin E and other antioxidants.
You will also find a cousin of this supplement sold as ubiquinol.

Coq10 benefit heart antioxidant and review of side effects and safety profile

CoQ10  benefit for the human body
CoQ10 is a naturally occurring component present in living cells. Its physiological function is to act as an essential cofactor for ATP production, and to perform important antioxidant activities in the body. In most countries, CoQ10 has been widely used as a dietary supplement for more than 30 years. Recently, the use of CoQ10 as a dietary supplement has grown with a corresponding increase in daily dosage. The published reports concerning safety studies indicate that CoQ10 has low toxicity and does not induce serious adverse effects in humans. Evidence from pharmacokinetic studies suggest that exogenous CoQ10 does not influence the biosynthesis of endogenous CoQ9 / CoQ10 nor does it accumulate into plasma or tissues after cessation of supplementation. Overall, these data from preclinical and clinical studies indicate that CoQ10 is safe for use as a dietary supplement.

CoQ10 supplement sellers
CoQ10 is sold by a number of vitamin companies.
Natural Factors easy-to-swallow Coenzyme Q10 softgel capsules contain a  high potency formula consisting of 100 mg of Coenzyme Q10 in a base of rice bran oil for enhanced absorption. CoQ10 or Ubiquinone is a natural substance essential to cellular energy production.  It is an antioxidant which scavenges free radicals throughout the body.  It is also involved in maintaining normal heart function. CoQ10 works well with Vitamin E and other antioxidants. All Natural Factors products are manufactured according to Canadian Health Protection Branch Good Manufacturing Practices (GMP), among the highest standards in the world.
Nature's Way has a good CoQ10 product.

Effect of smoking on levels
Concentrations of blood vitamin A, C, E, coenzyme Q10 and urine cotinine related to cigarette smoking exposure
Korean J Lab Med. 2009 Feb;29(1): Song SM, Park YS, Lee A, Cho YG, Kim DS, Lee HS, Choi SI, Lee KR. Seoul Clinical Laboratories, Seoul, Korea.
In smokers, smoking causes many disease entities including cancers, chronic pulmonary diseases and cardiovascular diseases. Passive smoking is also accepted as a carcinogen and its adverse health effects are emphasized. We measured blood vitamin A, C, E (alpha-, beta- and gamma-tocopherol), coenzyme Q10 and urine cotinine concentrations in nonsmokers and smokers. Twenty-one healthy nonsmokers and 24 healthy smokers were included in this study. Smoking status was assessed with a self-reported questionnaire. Plasma was analyzed for coenzyme Q10 and serum for vitamin A, C, E using HPLC (Agilent Technologies Inc., USA) and random urine for cotinine using LC/tandem mass spectrometry (Applied Biosystems Inc., Canada). Smokers had significantly lower serum concentrations of vitamin C than nonsmokers. No significant differences in concentrations of serum vitamin A, E, and plasma coenzyme Q10 were observed. Smokers had highly elevated urine cotinine levels. In 16 (76%) of 21 nonsmokers, urine cotinine was detected. The correlations between urine cotinine and blood antioxidants levels were not found. Neither, the correlation between smoking status and blood antioxidants & urine cotinine was found. This study shows that smokers had significantly lower vitamin C levels among nonenzymatic antioxidants, namely, vitamin A, C, E and coenzyme Q10. High detection rate of urine cotinine in nonsmokers show the seriousness of passive smoking exposure, therefore more social efforts should be directed to reduce passive smoking exposure.