What would make your heart not suitable for sex (as referenced in many ED treatment commercials)?

Sex. Severe hemodynamic or arrhythmic heart disease can made sexual activity risky.
Sex and ED. This is a very individual matter as there are many diseases and many medications for heart disease that would make it dangerous to participate in sexual activity and/or other vigorous activity. You should discuss this thoroughly with your physician to determine what activity is safe for you in your situation.