He was clean when he died and one of the paramedics who tried to save his life was Tasha Starkey, who posted a picture of the note on Twitter, reports the Daily Mail.
John Hagans, a nurse consultant at the charity, said they were "disgusted" by the note.
He said: "Words fail me. This person deserves to be shamed. If the person who wrote it had had any idea of what was going on inside, they would not have dared.
"The resident collapsed in the home and was vomiting blood and our nurses and the ambulance crew battled extremely hard to save him.
"His condition was so severe they could not move the ambulance for half an hour because they were fighting so hard to save him.
"In that situation no ambulance crew should have to worry about annoying others because of parking. It's ridiculous.
"One of our staff members who was trying to help them spotted the note when they brought him to the ambulance. We were left completely stunned.
"What's worse is that another driver was trapped on an alleyway that runs down the back of our property for over 40 minutes.
"They did not say a word. They just respectfully sat in the car and waited, as you would hope anyone would do."
He added: "I feel so sorry for the man's family, knowing that the note was placed on the ambulance that tried to save their son. Our thoughts and prayers are with them."
The patient passed away at Heartlands Hospital on Friday evening.
Residents on the street in the Small Heath area of Birmingham expressed their disgust at the note.
Anamaria Dunne said: "I did not see the ambulance come but my husband did. He said there was nowhere else it could go.
"It's not nice that they left the note when the ambulance crew is trying to save someone's life.
"But there are real problems with parking around here. People's drives get block a lot and it's incredibly frustrating.
"Sometimes people will park on their neighbour's driveways just because there is not enough space. It's a real problem."
Another neighbour, who did not wish to be named, said: "It's a ridiculous situation here. You see arguments in the streets about it sometimes.
'In a way I'm not surprised someone left an angry note, even though it is shocking to do it to an ambulance.
"There are too many people parking poorly."
Paramedic Tasha Starkey was first to share an image of the offending note on Twitter on Friday afternoon in a post saying: "Crew alerted an extremely poorly patient to hospital... minimal on scene time, arrived at hospital to find this note... this patient was TIME-CRITICAL."
Paramedic Clinical Team Mentor Sam Grimson wrote: "One of our crews encountered this delightful note after assisting a patient suffering a major internal bleed! The crew were not on scene long due to how poorly the patient was.
"We always try to park appropriately but sometimes it is not possible."
West Midlands Ambulance Service tweeted: "Sometimes we just don't know what to say. This was the note left on an ambulance today. At the time, the crew were helping a man who was extremely unwell after vomiting blood.
"They took him on blue lights to hospital where he was in a critical condition. #patientscomefirst"
In a second separate incident over the weekend, the service was targeted by another angry resident understood to be complaining about an ambulance being parked in a place that prevented their car from moving.
A post read: "Just heard from one of our staff that two crews were treating a cardiac arrest patient today - the most serious case we can attend - and someone banged on the side of the ambulance asking them to move as they couldn't get their car out! Sorry #patientscomefirst #sad"
West Midlands Police also tweeted that a marked police vehicle had been damaged at a Remembrance Sunday event and its windscreen smashed.
